Shamrock made his World Wrestling Federation (WWF) debut as a face on the February 24, 1997 episode of Monday Night Raw. On March 23, 1997, Shamrock, billed as "The World's Most Dangerous Man", refereed a submission match between Bret Hart and Steve Austin at WrestleMania 13.
Shamrock returned to the ring following WrestleMania, squashing Vernon White in his debut WWF match. He went on to feud with Vader, Bret Hart, and The Hart Foundation throughout 1997. Shamrock's rivalry with the Harts led to his first WWF pay-per-view main event at In Your House 16: Canadian Stampede, and culminated in a bout between him and The British Bulldog for the European Championship at SummerSlam, which Shamrock lost by disqualification after hitting the Bulldog with a can of dog food. Shamrock went on to wrestle Bret Hart to a no-contest in a match for the latter's WWF Championship on the October 21 edition of Raw. He again challenged for the WWF Championship in the main event of December's D-Generation X: In Your House, defeating champion Shawn Michaels by disqualification when Triple H interfered.
Throughout early 1998, Shamrock feuded with The Rock and his Nation of Domination stable over Rock's Intercontinental Championship. He lost to Rock via disqualification at the Royal Rumble and a victory over him at WrestleMania XIV was reversed after Shamrock continued to apply his ankle lock after Rock had submitted.
In June 1998, Shamrock competed in the 1998 King of the Ring tournament, eliminating Nation members Mark Henry, Kama and The Rock, as well as Jeff Jarrett, to win the tournament. Following King of the Ring, Shamrock feuded briefly with the returning King Mabel, who had interfered to attack him in a rematch with Jarrett, and whom Shamrock defeated in a singles match injuring his leg. He next feuded with Owen Hart; Hart defeated Shamrock in a "Hart Family Dungeon match" at Fully Loaded, and Shamrock defeated Hart in a "Lion's Den match" at SummerSlam. In September, he formed a short-lived stable with Mankind and The Rock.
Shamrock turned heel in October 1998 and won the vacant Intercontinental Championship on October 12, defeating X-Pac in the finals of an eight-man tournament. In November, Shamrock joined Mr. McMahon's Corporation after McMahon offered him "a family" in exchange for his services. On December 14, Shamrock and fellow Corporation member The Big Boss Man defeated the New Age Outlaws for the WWF Tag Team Championship, making Shamrock a dual champion. The duo held the titles until January 25, 1999, when they lost to Jeff Jarrett and Owen Hart.
In January 1999, Shamrock began feuding with Billy Gunn, Goldust and Val Venis, all of whom had made overtures to his kayfabe sister, Ryan. He lost the Intercontinental Championship to Venis on February 14 at St. Valentine's Day Massacre when Gunn, the guest referee, delivered a fast count. Shamrock took part in a four way bout for the Intercontinental Championship at WrestleMania XV. The reigning champion, Road Dogg, was able to retain his title by pinning Goldust after Shamrock and Venis were counted out while brawling outside the ring.
In early mid-1999, the Corporation began feuding with The Undertaker and his Ministry of Darkness, with The Undertaker's minions repeatedly ambushing Shamrock and kidnapping Ryan, sacrificing her on the Undertaker's symbol. After breaking away from the Corporation, thus turning face once more, Shamrock went on to feud with The Undertaker at Backlash, and lost.
After losing to Undertaker, Shamrock, Big Show, Mankind and Test formed The Union, a stable of wrestlers in opposition to the Corporate Ministry. The Union dissolved soon after defeating the Corporate Ministry at Over the Edge in May. Shamrock briefly feuded with Jeff Jarrett before beginning a rivalry with martial artist Steve Blackman that saw he and Blackman fight one another in a series of unorthodox matches. The feud ended at SummerSlam, where Shamrock defeated Blackman in a "Lion's Den weapons match". He went on to feud with the newly debuted Chris Jericho until departing the WWF in late 1999. His departure was attributed on screen to an injury inflicted by Jericho's bodyguard, Mr. Hughes.