He caught the eye of the WWF where he made his debut in 1979 and won the first-ever Battle Royal in Madison Square Garden, New York City. This earned him a title shot at then-champion Bob Backlund, who pinned him later that night in a 30-minute battle. He later feuded with Chief Jay Strongbow and Bruno Sammartino before leaving in 1980.
The Iron Sheik returned to the WWF in 1983 and challenged Backlund once again; he defeated him on December 26, 1983 at Madison Square Garden for the WWF World championship. Sheik had supposedly injured Backlund during a "Persian club challenge" prior to this title match.
During his brief title reign, The Iron Sheik wrestled against Backlund, Chief Jay Strongbow, Pat Patterson, and Tito Santana before dropping the belt just four weeks later to Hulk Hogan. He would then engage in a bitter feud with Sgt. Slaughter, to whom he would eventually lose a "Boot Camp Rules" match. As a tag team partner with Nikolai Volkoff, and under the management of "Classy" Freddie Blassie, the newly-dubbed "Foreign Legion" won the WWF World tag team title from the U.S. Express at the first WrestleMania. Part of the pair's regular entrance consisted of waving the Iranian and Russian flags, then demanding that the crowd be quiet and "show respect" while Volkoff sang a throaty version of the Soviet national anthem, a demand that usually only attracted boos from the crowd. Sheik then usually grabbed the mic and said "Iran number 1, Russia number 1, USA (followed by a simulated spitting act)." It was all designed to get major heat from the crowd.
In 1987, he was released along with Jim Duggan. In 1988, The Iron Sheik returned to the WWF but the return was short-lived.
He returned to the WWF again in 1991, making his re-debut on Wrestling Challenge as Colonel Mustafa, and was aligned with former enemy Sgt. Slaughter. Along with Iraqi General Adnan, Slaughter and Mustafa were portrayed as Iraqi sympathizers during the first Gulf War and feuded with Hulk Hogan and the Ultimate Warrior. Following Slaughter's face turn after SummerSlam 1991, he teamed with General Adnan until the middle of 1992, when he left the promotion again.
In late 1996, the Sheik would team up with his old nemesis Bob Backlund to manage WWF wrestler The Sultan, who had a Middle Eastern gimmick, however, he was released soon after.
On April 1, 2001, at WrestleMania X-Seven, the Iron Sheik was the victor of the Gimmick Battle Royal, a match between other popular or outlandish wrestlers from the 1980s and 1990s. Reportedly the Iron Sheik was chosen to be the winner because he was physically unable to take the "over the top rope" move that eliminated each competitor. Rather than being booed for winning, the villainous Sheik was cheered as a fan favorite.
In 2005, the Iron Sheik was inducted into the WWE Hall of Fame by his old rival, Sgt. Slaughter. On the June 11, 2007 episode of Raw, he along with Jimmy Snuka appeared in a taped segment showing their appreciation of WWE owner Vince McMahon. On the June 18 episode of Raw, he approached McMahon's executive assistant Jonathan Coachman about having his own interview show on Raw. Coach replied saying, "I like the idea and I will really take some time to consider it." On August 13, he appeared on an episode of Raw held at Madison Square Garden for a WWE version of American Idol. Sheik came out with Nikolai Volkoff while Volkoff sang the Soviet anthem. The March 10, 2008 edition of Raw featured rematches from previous WrestleManias. Iron Sheik appeared with Nikolai Volkoff to face off against the U.S. Express in a rematch from the first WrestleMania. Before the bout could begin, they were interrupted by Jillian Hall.
On October 2, 2009, on the 10th anniversary of Smackdown, he appeared backstage arguing with Sgt. Slaughter, choking on a shrimp, then helped by Hurricane Helms.
He made an appearance on WWE Monday Night Raw on November 16, 2009 in the opening of the show, with Rowdy Roddy Piper and Luis Guzmán, going nuts on Hulk Hogan and proving his dominance with a LJN WWF action figure of himself and Hulk Hogan.
On the November 15, 2010, edition of Raw, as part of the Old School theme, Iron Sheik appeared with Nikolai Volkoff, singing the Soviet national anthem before being interrupted by Santino Marella and Vladimir Kozlov, the latter of whom then sung a duet with Volkoff of the Russian National anthem. He then proceeded to rant on Hulk Hogan until his microphone was cut off.