In 1990, Cassidy, as Steve Armstrong, went to World Championship Wrestling alongside Tracy Smothers, and feuded with The Fabulous Freebirds (Michael Hayes and Jimmy Garvin). In 1991, they changed their name to The Young Pistols and they became heels and won the U.S. Tag Team Titles.
In 1992, Armstrong came to the WWF as Lance Cassidy, under a babyface cowboy gimmick. He made his television debut on the October 10, 1992 episode of Superstars, beating Tom Stone. The run proved to be short, as after only a few television appearances and some house show victories over Skinner and Terry Taylor, he left the WWF in January 1993.
On April 25, 1995, he returned to work for WCW and wrestled Craig Pittman at a WCW Saturday Night episode. In July, he began teaming with his brother Scott as The James Boys. At the July 10 taping of WCW Pro, WCW Tag Team Champions Bunkhouse Buck and Dick Slater defeated the duo in their debut match. A month later on the August 5 edition, they fell to Arn Anderson and Ric Flair. On August 22, they faced Men at Work, but were again unsuccessful. Steve made his return to pay-per-view when he appeared at WCW World War 3 on November 26, 1995, when he competed in the three ring battle royal.
Although back as a performer in WCW, he was mainly used as a jobber working with his brother Scott as The Armstrongs or James Brothers on Saturday Night, WorldWide and, on rare occasions, on Monday Nitro. On the February 17 edition of WCW Saturday Night, they again fell to Men at Work. In June 1996, they were defeated by Public Enemy, and on the July 1 edition, they were defeated again by Arn Anderson and Ric Flair. On the July 28, 1996 edition of WCW WorldWide, they fell to Lord Steven Regal and Squire Dave Taylor. On the August 22 taping of WCW Pro, The Armstrong Brothers would finally gain their first WCW victory when they defeated Bill Payne and Rick Thames. They would go on to face The Amazing French Canadians and The Faces of Fear during the remainder of 1996.
The Armstrong Brothers would continue teaming in 1997 and faced The Amazing French Canadians and The Steiner Brothers. On the April 13 edition of WCW WorldWide, they defeated The Southern Posse. After this they moved on to a brief series of matches with Harlem Heat, and in May 1997, they defeated the new duo of Jim Powers and Bobby Walker, the latter put together by Teddy Long. After this, they were winless for the rest of 1997 in matches with Mortis and Wrath, as well as The Public Enemy. Their pairing continued into 1998 but again saw little success. They were winless against High Voltage in multiple encounters. On the September 13 pay-per-view Fall Brawl 1998, they were involved in an angle when WCW WorldWide announcer Mike Tenay attempted to interview them, only to be interrupted by Ernest Miller, who then attacked both brothers. Thirteen days later, they would defeat The Power Company on WCW Saturday Night. On November 30, 1998, the duo enjoyed the biggest victory of their WCW tenure when they upset Raven and Kanyon on WCW Monday Nitro.
Success continued for The Armstrong Brothers in 1999. On January 6, they upset Alex Wright and Disco Inferno in Mobile, Alabama. On the January 9 edition of WCW Saturday Night, they defeated Nick Dinsmore and Mike Sullivan. The winning streak was stopped in April on WCW Saturday Night when they were defeated by Disorderly Conduct. On April 27, at a television taping in Bismarck, North Dakota, they faced the NWO for the first time and defeated Vincent and Stevie Ray. On April 29, on WCW Monday Nitro, the team faced Raven in a handicap match and were victorious. Scott's teaming with Steve finally came to an end on March 1, 2000, when The James Brothers faced WCW World Tag Team Champions Big Vito and Johnny the Bull at a WCW Saturday Night taping.
On March 29, 2000, Steve made his last television appearance for the promotion as he lost to Hugh Morrus on Saturday Night.