After winning several stand-up comedy competitions, Hart had his first breakthrough when Judd Apatow cast him in a recurring role on the TV series Undeclared (2001).

Hart's comedic reputation continued to grow with the release of his first stand-up album I'm a Grown Little Man (2009).

[2] He was raised in a single-parent household by his mother, who worked as a systems analyst for the Office of Student Registration and Financial Services at the University of Pennsylvania.

[7][8][9] After graduating from George Washington High School, Hart briefly attended the Community College of Philadelphia before dropping out and moving to New York City.

[12][13] Hart's first stand-up performance took place at The Laff House in his native Philadelphia under the name of Lil Kev, which did not go well.

[15] After those initial unsuccessful shows, he began entering comedy competitions throughout Massachusetts, with audience receptions eventually improving.

After an early period of attempting to imitate comedians like Chris Tucker, he found his own rhythm by delving into his insecurities and life experiences.

"[15] Hart's comedy tours began in 2009 with his act titled I'm a Grown Little Man, followed by Seriously Funny in 2010, Laugh at My Pain in 2011, and Let Me Explain in 2013, the last two of which were also released as features in movie theaters.

Hart then had other films roles such as the Scary Movie franchise, Soul Plane, The 40-Year-Old Virgin, Death at a Funeral and Little Fockers.

In 2013, Hart played a boxing promoter in Grudge Match and appeared in Exit Strategy as Mannequin Head Man.

[28] The show follows Hart along with other married celebrities (each playing a comical fictionalized version of themselves) within the series including: Boris Kodjoe, Nelly, Duane Martin, J.B. Smoove, Nick Cannon and Robin Thicke.

Under the deal, Hart and his HartBeat Productions banner will develop and produce live-action, scripted kids content for the network.

[38] Hart also reprised his role of Snowball in the sequel The Secret Life of Pets 2, and Franklin Finbar in Jumanji: The Next Level.

In 2021, Hart starred in Fatherhood, a drama about a man whose wife dies shortly after childbirth, leaving him to raise their daughter on his own.

[42] He later played Arnold Drummond in the Diff'rent Strokes portion of the third edition of Live in Front of a Studio Audience.

The movie shows how Sonny (Hart) experiences a wild journey with his friend after finding a much-longed-for free weekend.

[49] In 2017, Hart founded Laugh Out Loud (LOL),[50] a global media and production company to provide opportunities for top comedic talent of all ethnicities worldwide.

[53] Hart has aggressively expanded LOL's reach since its founding, securing partnership deals with PlutoTV, Roku, Snap, Facebook, Peacock, and YouTube.

[55][56][57] Known for content such as Cold As Balls, What the Fit, Die Hart, and more, LOL has amassed more than 1 billion video views across its digital platforms,[58] and has worked with brand partners such as AT&T, Headspace, Lyft, Old Spice, P&G, and Viacom.

[60] Hart then hosted the 2012 MTV Video Music Awards,[61] after his longtime friend Judd Apatow, the director who gave him his first big on-screen break in the TV series Undeclared, recommended him for the position.

[71] On January 3, 2019, Hart stated that he was going to reconsider stepping down as host, after openly lesbian comedian Ellen DeGeneres, who has hosted the Academy Awards multiple times, expressed support for him to do so and said she had contacted the Academy to ask if Hart would be able to reverse his decision if he wished and, according to DeGeneres, they said he would be able to do so.

[72] On January 8, following backlash for what was perceived as an insincere apology by critics, Hart confirmed that he would not be hosting the Academy Awards.

[80][81] The restaurant's offerings are claimed to be "entirely free of cholesterol, antibiotics, hormones, artificial colors, preservatives, high-fructose corn syrup, or trans fats", and inspired by Hart's own "health nut" lifestyle.

[84] Hart has cited George Carlin, Dave Chappelle, Bill Cosby, Eddie Murphy, Patrice O'Neal, Richard Pryor, Keith Robinson, Chris Rock, and Jerry Seinfeld as his influences.

[99] On September 1, 2019, Hart was a passenger in a 1970 Plymouth Barracuda that went off Mulholland Highway and rolled down an embankment near Calabasas, California.

[101] On August 23, 2023, Hart ran a 40-yard race with former National Football League running back Stevan Ridley, and tore his lower abductors on his abdomen.

He required a wheelchair as part of his recovery and said afterward he is the "dumbest man alive" and "the age 40 is real", recommending no one attempt to race like he did.

[102] On April 14, 2013, Hart was charged on suspicion of drunk driving after his vehicle nearly collided with a tanker truck on a Southern California freeway.