Geary made his first appearance on television in an episode of Room 222 and later appeared in All in the Family, The Mod Squad, Mannix, Marcus Welby, M.D., The Streets of San Francisco and Barnaby Jones. Geary's first daytime role was in NBC soap opera Bright Promise from 1971 to 1972.

He played George Curtis, who was a rapist, in The Young and the Restless and in 1978 was hired for a 13-week story arc to play Luke Spencer in ABC soap General Hospital. His character in General Hospital began as a hit man and later as a rapist who fell in love and subsequently married his victim, Laura Webber (played by Genie Francis). His portrayal of Luke Spencer on General Hospital was well received and grew into a full contract role. The 1981 on-screen wedding of his character and Laura Webber holds the record as the highest rated soap opera episode of all time.

He holds the distinction of winning a record eight Daytime Emmy Awards for Outstanding Lead Actor in a Drama Series. He was first nominated in 1980, 1981, and had his first win in 1982. Geary was nominated again in 1983, before leaving the show in 1984. Over the next several years he took roles in various theater and television productions, as well as in several films, but not at the level of success he had hoped for. Despite the popularity of his work as Luke Spencer, filmmakers such as Oliver Stone pigeonholed Geary based solely on the fact that he was a "soap actor". In a conscious effort to distance himself from GH, he actively sought a role in "Weird Al" Yankovic's film debut UHF (1989), that of the quietly eccentric scientist Philo (named for television pioneer Philo Farnsworth). Geary, a fan of Yankovic, went so far as to grow his hair like Albert Einstein's and stay in character as Philo when meeting the film's casting team; he immediately landed the part.

A notable exception from his series of dramatic roles is the part of a scientist/studio Engineer in the comedy/spoof movie UHF. He also appeared in 1987's Disorderlies, with Rappers the Fat Boys.

In 1991, Geary returned to General Hospital as Luke's cousin and look-alike Bill Eckert, due to the actor's Desire to play something other than Luke. However, due to poor feedback from the viewing public, the character was killed off and Geary resumed the role of Luke in 1993. Tony appeared in more than 50 stage plays, including an award-winning one-man show titled Human Scratchings in 1996. He was nominated in 1997 and 1998 for Daytime Emmys for Outstanding Lead Actor, and had his second win in 1999, and his third in 2000. He received another nomination in 2003, and had his fourth win in 2004. When Geary won for the fifth time in 2006, he set the record for most lead actor wins. Geary received another Emmy nomination in 2007, and in 2008, he again set a record for most lead actor wins with his sixth Emmy for Outstanding Lead Actor.

Anthony Geary was born in Coalville, Utah, a son of Dana (née Anderson) (2/10/1923–7/7/1997) and Russell Dean Geary (11/12/25–10/8/1991). His father was a building contractor and owner of a construction company. His mother was a homemaker and assisted his father in the Business as the bookkeeper. His father was also the former mayor of Coalville, Utah. Both of Geary's parents were members of the Church of Jesus Christ of Latter-day Saints. He has two sisters, Jana Geary Steele and DeAnn Geary Bond. Geary attended the University of Utah, Salt Lake City, on a theater scholarship. At age 21, he performed as a chorus boy with Sid Caesar and Imogene Coca on the Las Vegas stage. It was while performing there that he fell and scarred his chin.

Geary set a record in 2012 with his 7th Daytime Emmy win and again in 2015 for his 8th win for Outstanding Leading Actor in a Drama Series after 16 nominations for the same role of General Hospital's Luke Spencer. Geary publicly announced on Friday, May 8, 2015 that he would be leaving his role on General Hospital. Geary finished taping his last scenes on the General Hospital set on Tuesday June 23, 2015. His last airdate was July 27, 2015.