[1][6] After graduating from Glenbard West High School,[7] Hayes attended Illinois State University,[6] where he studied piano performance.

[8] He left "two or three classes short" of graduation when he became music director at the Pheasant Run Theater in St. Charles, Illinois.

[11] He moved to Los Angeles in 1995,[10] where he found work as a comedian and an actor on stage and on television, including a commercial for Doritos which aired during Super Bowl XXXII in 1998.

He made his professional debut in the independent film Billy's Hollywood Screen Kiss (1998), which brought him wide attention.

[12] The same year, he was cast as Jack McFarland, a flamboyantly gay and frequently unemployed actor, in the NBC comedy series Will & Grace.

The show became a long-running hit and Hayes' performance earned him seven consecutive Emmy Award nominations as Outstanding Supporting Actor in a Comedy Series.

He also executive produced The Sperm Donor and Stephen's Life, the two winning scripts that were chosen by NBC.

[17] Hayes starred in the Broadway production An Act of God, June 6 to September 4, 2016, after engagements in Los Angeles and San Francisco.

In February 2025, it was announced that Hayes would make his debut on the West End reprising this role in a production at the Barbican Theatre in the summer of 2025.

[25][26][27][28] Hayes was co-executive producer of the TV Land original comedy series Hot in Cleveland, which premiered in June 2010 and ran for six seasons.

[28] Hayes and his husband, Scott Icenogle, produce lip-sync videos under their YouTube channel, The Kitchen Sync.

[33] In July 2020, Hayes, along with Will Arnett and Jason Bateman, created a comedy and talk podcast called SmartLess.

Hayes refused to discuss his sexual orientation for many years, saying he believed that audiences would therefore be more open-minded about his characters.

In response to a satirical piece run in The Advocate, which criticized him for being opaque about his sexual orientation, he appeared to imply that he is gay, stating: "Really?

"[10] After he received Outfest's Trailblazer Award in 2016 he addressed this criticism in his speech, saying in part: "Looking back at my choice to stay silent, I am ashamed and embarrassed.

[38] In October 2017, while appearing on an episode of The Ellen DeGeneres Show, Hayes revealed that he had been hospitalized with a rare condition in which his small intestine burst.

[39] Hayes has been open about living with atrial fibrillation, a cardiac disorder that causes him to frequently visit the ER to get his heart shocked back into sinus rhythm whenever his heartbeat is too irregular or rapid.