In 2014, Morgan signed a contract with WWE, assigning her to their developmental territory, NXT, in October 2014. She made her first televised appearance at the NXT TakeOver: Rival event on February 11, 2015, as a planted fan, who jumped on Tyler Breeze during his ring entrance. She later appeared at NXT TakeOver: Unstoppable on May 20, again as part of Breeze's entrance. In October 2015, she briefly worked under the ring name Marley, debuting on the November 4 episode of NXT, where she worked as a jobber losing to Eva Marie.
On the December 2, 2015 episode of NXT, Marley made her return under the new ring name Liv Morgan, losing to Emma. On the January 13, 2016, episode of NXT, Morgan competed in a battle royal to determine the number one contender to Bayley's NXT Women's Championship, which was won by Carmella. On the August 17 episode of NXT, she competed in a six-woman tag team match, along with Carmella and Nikki Cross, in which they defeated Daria Berenato, Mandy Rose and Alexa Bliss. On the August 31 episode of NXT, Morgan picked up her first televised singles win, defeating Aliyah. On the September 14 episode of NXT, Morgan defeated Rachel Fazio in singles competition via submission, and would issue a challenge to the NXT Women's Champion Asuka. The following week, however, Morgan was submitted by Asuka in under a minute, and would afterwards begin a rivalry with The Iconic Duo (Billie Kay and Peyton Royce), with both women confronting her following her match, leading to match between Morgan and Kay two weeks later, with Kay picking up the victory after interference by Royce. On the October 26 episode of NXT, she interrupted a match between Kay and Aliyah by attacking Royce, causing a distraction that allowed Aliyah to defeat Kay. Morgan went on to compete against Royce on the November 16 episode of NXT, which ended in a disqualification after Kay interfered in the match, attacking Morgan and Aliyah until Ember Moon made the save. The three faced off in a six-person tag team match against Kay, Royce, and Daria Berenato on the November 23 episode of NXT, with Morgan's team coming out victorious.
On the November 21, 2017, episode of SmackDown Live, Morgan made her main roster debut along with Ruby Riott and Sarah Logan, attacking both Becky Lynch and Naomi. On the same night, they interrupted a match between SmackDown Women's Champion Charlotte Flair and Natalya, then proceeded to attack both of them. The following week on SmackDown Live, the trio, now called "The Riott Squad", made their in-ring debuts for the brand, defeating Flair, Natalya, and Naomi in a six-woman tag team match. On January 28, 2018, Morgan participated in the first women's Royal Rumble match at the Royal Rumble pay-per-view as the eleventh entrant, but was eliminated by Michelle McCool.
On April 16, The Riott Squad were drafted to Raw, as part of the 2018 Superstar Shake-Up and caused the match between Bayley and Sasha Banks to end in a no contest. On the September 24 episode of Raw, Morgan was legitimately knocked unconscious by Brie Bella when Bella was doing Yes Kicks and two of them connected to her head; Morgan would continue for a bit before being taken out of the match. On September 24, Morgan was diagnosed with a concussion and would go through WWE's concussion policy, putting her participation in the match with The Riott Squad against Raw Women's Champion Ronda Rousey and The Bella Twins at Super Show-Down in jeopardy. In the first ever all women's pay–per–view Evolution, The Riott Squad lost to Natalya, Bayley and Sasha Banks.
In 2019, Morgan participated in the women's Royal Rumble match, only to be the first to be eliminated after lasting 8 seconds, setting the record for the shortest time in the women’s Royal Rumble match. One month later, on February 17, Morgan and Logan competed in a six–team Elimination Chamber match for the inaugural WWE Women's Tag Team Championship at the namesake pay–per–view, where they were the third team eliminated by Nia Jax and Tamina but the eventual winners were Sasha Banks and Bayley. On April 7, Morgan competed at WrestleMania 35 in the WrestleMania Women's Battle Royal, which was eventually won by Carmella.
On April 16, 2019, during the 2019 WWE Superstar Shake-up, Morgan was moved to the SmackDown brand, separating her from The Riott Squad in the process. On the July 16, 2019 episode of SmackDown, she debuted and confronted Charlotte Flair. This lead to a match between the two, in which Morgan lost by submission. This was her first match outside of house shows since WrestleMania 35 in April. Following this match, Morgan was kept off of television for the rest of her time on SmackDown.
On the October 14 episode of Raw, Morgan was the final overall pick of the 2019 WWE draft, being drafted to the Raw brand. On the December 9 episode of Raw, a vignette aired promoting Morgan's return and debut on the Raw brand. She returned to television on the December 30 episode of Raw, during Bobby Lashley and Lana's storyline wedding, interrupting the proceedings and professing her love for Lana. After Lana subsequently attacked her, she aligned herself with Rusev. On the January 27, episode of Raw, Morgan defeated Lana, and once again defeated her the next week, only to be attacked by a returning Ruby Riott. This led to a match between the two on the March 2 episode of Raw, where Morgan was victorious, only to be attacked by special guest referee Sarah Logan afterwards.
At Elimination Chamber on March 8, Morgan entered her second Elimination chamber match to determine Becky Lynch's WrestleMania 36 challenger, but was unsuccessful after being eliminated by eventual winner Shayna Baszler. The following night on Raw, Morgan attacked Riott and Logan during a tag team match. On the WrestleMania 36 kickoff show, Morgan defeated Natalya. The night after on Raw, Morgan faced Asuka in a losing effort. On the April 20 episode of Raw, she defeated her former tag team partner Ruby Riott. The following week, Liv defeated Ruby a third time. On the May 4 episode of Raw, Liv Morgan confronted NXT Women's Champion Charlotte Flair, which led to a match between the two, in which Morgan lost. Morgan would then go on a losing streak losing to The IIconics in a tag team match with Natalya on the June 15 episode of Raw, and losing to Natalya the following week. Riott would attempt to console Morgan backstage after her loss but Morgan would immediately reject her.
On the August 3, 2020 Raw, Ruby appeared on the Kevin Owens Show and apologized to the returning Liv Morgan, only to be interrupted by the IIconics. Later the same night, Liv decided to team up with Riott to take on the IIconics in a winning effort. At Payback, Morgan and Riott (now officially known as The Riott Squad again) defeated The IIconics, and once more the following night on Raw, forcing The IIconics to disband, per stipulation. As part of the 2020 draft in October, both Morgan and Riott were drafted to the SmackDown brand. She would go on to win a fatal four-way match during her first night on SmackDown after the Draft to qualify for the women's team at Survivor Series. After Survivor Series, both Riott and Morgan would go on a tag team winning streak.They challenged for a shot at the tag team titles at WrestleMania 37, but failed to win the match. On June 2, 2021, Riott was released by WWE, effectively disbanding The Riott Squad for the second time.
On the June 4 episode of SmackDown, Morgan returned to singles competition by facing Carmella in a losing effort. The following week, they had a rematch in which Morgan was finally able to defeat Carmella. Morgan began to take issue with Sonya Deville for adding Carmella and a returning Zelina Vega to the women's ladder match at Money in the Bank. She defeated Carmella and Vega in single matches before she took Carmella's spot in the ladder match, with Carmella instead competing against Bianca Belair for the SmackDown Women's Championship. On the September 17 episode of SmackDown, Morgan teamed with Toni Storm to take on Zelina Vega and Carmella. The match would end via countout, which would then lead to Morgan challenging Carmella to a match at Extreme Rules, which Morgan won.
As part of the 2021 Draft, Morgan was drafted to the Raw brand. In October, Morgan entered the Queen's Crown tournament, where she lost to Carmella in the first round. On the season premiere of Raw, Carmella defeated Liv Morgan. The next week, Liv Morgan confronted the Raw Women’s Champion Becky Lynch. On the November 8 edition of Raw, Morgan competed in a fatal five-way to become the number one contender for the Raw Women’s Championship, in a match including Zelina Vega, Carmella, Rhea Ripley, and Bianca Belair. Morgan won the match by pinning Carmella to become the number one contender to Becky Lynch. She would receive her title match against Lynch on the December 6 episode of Raw, where Lynch retained the title. In a rematch at WWE Day 1, Lynch defeated Morgan again.
On the June 13 episode of Raw, Morgan teamed with Alexa Bliss to defeat Doudrop and Nikki A.S.H. in a tag team match to qualify for the women's Money in the Bank ladder match. At the event, on July 2, Morgan won the Money in the Bank contract, granting her a match of her choice for either the Raw or SmackDown Women's Championship. Later that night, following the SmackDown Women's Championship match between Natalya and Ronda Rousey, Morgan cashed in her contract on the latter to win the title, making her the third woman, next to Alexa Bliss and Bayley, and the fifth wrestler overall, to cash-in the Money in the Bank contract the same night after winning it. At SummerSlam on July 30, Morgan controversially retained the title in a rematch against Rousey; Morgan tapped out to Rousey's armbar, but the referee had counted Rousey's shoulders down, giving the pinfall win to Morgan. After the match, both Morgan and the referee were attacked by Rousey. At Clash at the Castle on September 3, Morgan successfully retained the title against Shayna Baszler. Rousey then won a fatal five-way elimination match on the September 9 episode of SmackDown, earning a rematch against Morgan at Extreme Rules. The following week, Morgan challenged Rousey to an Extreme Rules match for the title, which Rousey accepted. At the event on October 8, Morgan lost the SmackDown Women's Championship back to Rousey, ending her reign at 98 days.
Morgan then entered the women's Royal Rumble match at the titular event on January 28, 2023. She entered at number two and lasted over one hour before being the last one eliminated by the match's winner and first entrant Rhea Ripley. She then took part in the women's Elimination Chamber match at the titular event on February 18, but was eliminated by Natalya and Asuka. On Night Two of WrestleMania 39, Morgan teamed with Raquel Rodriguez to take part in the women's WrestleMania Showcase fatal four-way tag team match, which was won by Ronda Rousey and Shayna Baszler. The following night on Raw, Morgan teamed with Rodriguez to defeat Damage Control in a number one contenders match for the WWE Women's Tag Team Championship, with the match being scheduled for the following week against reigning champions Lita and Becky Lynch. On the April 10 episode of Raw, they won their title match and became the new Women's Tag Team Champions, with Morgan winning the title for the first time individually. On the April 21 episode of SmackDown, Morgan and Rodriguez retained their titles against Sonya Deville and Chelsea Green. Morgan and Rodriguez were both drafted to Raw during the 2023 WWE Draft. On the May 19 episode of SmackDown, Morgan and Rodriguez vacated the titles due to Morgan suffering an injury, ending their reign at 39 days.
Morgan would make her return on the June 23 episode of SmackDown. The following day, on SmackDown LowDown, it was announced that Morgan and Rodriguez would challenge Rousey and Baszler for the WWE Women's Tag Team Championships at Money in the Bank. At the event on July 1, Morgan and Rodriguez faced off with Baszler and Rousey for the titles and would ultimately win after Baszler turned on her partner and attacked Rousey, opening the door for Morgan to pin her and win the match, earning Morgan and Rodriguez their second reign as the Women's Tag Team Champions. On the July 17 edition of Raw, Morgan and Rodriguez lost the WWE Women's Tag Team Championships to Sonya Deville and Chelsea Green, ending their second reign at sixteen days. The following week, Morgan was scheduled to face Rhea Ripley, however, the match never began as Ripley viciously attacked Morgan with a steel chair.
After a six month hiatus, Morgan returned at the 2024 Royal Rumble, entering the Royal Rumble match at number thirty. Morgan went on to be the runner-up in the match for a second year in a row, eliminating Zoey Stark and Jade Cargill in the process, before being eliminated by the winner, Bayley. She then took part in the women's Elimination Chamber match at the titular event, but was the last woman eliminated by Becky Lynch. On the April 8 episode of Raw, Morgan attacked Rhea Ripley in a backstage segment, during which Ripley legitimately injured her right arm and was forced to vacate the Women's World Championship. The following week, on the April 15 episode of Raw, Morgan interrupted Ripley's announcement that she was vacating the Women's World Championship, to which she would laugh and mock, while simultaneously being held back by security. Later on, while being interviewed backstage, she stated that it was "karma" for Ripley injuring her for several months as justification for her attack. Over the next few weeks, Morgan began to display more villainous traits. At King and Queen of the Ring on May 25, Morgan defeated Lynch to win the Women's World Championship for the second time after accidental interference from Dominik Mysterio. Two nights later on Raw, Morgan defeated Lynch in a steel cage match to retain her title after another accidental interference from Mysterio, before kissing Mysterio on the lips after the match concluded. One week later, she continued her pursuit of Mysterio, believing him to have intentionally assisted her in her victories over Lynch, though members of the Judgment Day attempted to keep the two separated. On the June 24 episode of Raw, Morgan helped Finn Bálor and JD McDonagh defeated The Miz and R-Truth for the World Tag Team Championship. At SummerSlam on August 3, Morgan defeated Ripley to retain her title after interference from Mysterio, giving Ripley her first pinfall loss since May 2022. After the match, Mysterio kissed Morgan. On the following episode of Raw, Morgan officially joined The Judgment Day as Ripley and Damian Priest were excommunicated from the group. At Bash in Berlin on August 31, Morgan and Mysterio lost to Ripley and Priest in a mixed tag team match despite interference from Bálor, McDonagh and Carlito, with Ripley pinning Morgan. At Bad Blood on October 5, Morgan lost to Ripley by disqualification but retained her title after a returning Raquel Rodriguez attacked Ripley and allied herself with Morgan and The Judgment Day. At Crown Jewel on November 2, Morgan defeated WWE Women's Champion Nia Jax to win the inaugural WWE Women's Crown Jewel Championship after interference from Mysterio and Rodriguez.