Thompson began his acting career in the early 1990s, and was an original cast member of Nickelodeon's sketch comedy series All That (1994–2005), where he often collaborated with co-star Kel Mitchell.

[9] He went on to star in the original run of All That for its first five seasons, playing such characters as Principal Pimpell, Miss Piddlin, Pierre Escargot, and Superdude.

[20] Thompson's celebrity impressions on SNL include Al Sharpton, Whoopi Goldberg, Bill Cosby, Charles Barkley, David Ortiz, O. J. Simpson, and Steve Harvey.

[22] In commemoration of his 20th anniversary on the show, Thompson received a star on the Hollywood Walk of Fame on August 11, 2022.

In 2009, Thompson was a regular voice actor in the Fox animated series Sit Down, Shut Up, portraying Sue Sezno who, like her last name, always says no.

[24] The series premiered on April 19, 2009,[24] but was canceled after only four episodes due to low ratings and poor reviews.

Thompson also guest-starred as Gus's estranged college singing buddy on the USA Network series Psych in the fourth-season episode "High Top Fade Out".

[25] In 2015, film ticketing website Fandango announced that Thompson would play their brand character, Miles Mouvay.

[26] On September 23, 2015, Thompson appeared on The Tonight Show Starring Jimmy Fallon alongside former All That co-star Kel Mitchell in which they reprised their popular Good Burger roles as "Ed" and "Lester Oakes, Construction Worker".

They later competed against one another in an episode of the revived Nickelodeon game show Double Dare that aired in November 2018.

The series, retitled Kenan, premiered in 2021 on NBC, featuring Thompson as a newly-widowed father determined to be a "super dad".

[30] He was nominated for the Primetime Emmy Award for Outstanding Lead Actor in a Comedy Series after its first season.

[38] In 2020, he became the spokesman for Universal Destinations & Experiences' "Let Yourself Woah" campaign,[39] and was set to host the 2020 White House Correspondents' Dinner before it was cancelled due to the COVID-19 pandemic.

In March 2022, AFA fully funded the launch of Twenty Two Entertainment, led by actors Michael Rainey Jr. and Gianni Paolo, best known from the Starz series Power Book II: Ghost.

[46] On August 21, 2024, Thompson appeared at the Democratic National Convention to perform a skit highlighting Project 2025 and tying it to the presidential candidacy of Donald Trump, claiming "You vote for him.

"[47][48][49] ^1 Thompson stood in for Simon Cowell, who was still recovering from a back injury the previous week that required him to rest under medical observation.