Pratt, best known for his role on The Hills, filed his candidacy at the City Clerk's Office on Tuesday. He said he decided to run because of dissatisfaction with the current administration.
"We have no other choice, so it's pretty simple. We can't do four more years of Karen Bass," he said.
Pratt announced his run on the anniversary of the Palisades Fire, which destroyed his home. He is running his campaign with a focus on criticizing the city government's response to the fire that destroyed his home.
"I want what everybody wants: quality of life, affordability, you can go on. Everything the mayor has said she wants to do. She's had four years to do it, and everything is worse," Pratt said.
Bass delivered her State of the City address on Tuesday at an event that resembled a campaign kickoff.
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Another potential candidate is Los Angeles County Supervisor Lindsey Horvath, who recently created an account on X under the name Lindsey for L.A.
In a statement, she said in part, "Being asked - by constituents, community leaders, and those longing for a better Los Angeles - to consider a run for Mayor at this time weighs heavily on my heart and my commitment to being of service... I am listening carefully and seriously both to those who are urging me to enter this race, and to those who are eager to continue the work we have begun together at the county."
Pratt said he hopes Horvath joins the race.
"I can't wait for her to announce, because I can't wait for those two to argue about who's worse at their job. They're both career politicians that have continued to fail taxpayers," he said.
Former Los Angeles Unified School District Superintendent Austin Beutner has also declared his intentions to run for mayor. Billionaire developer Rick Caruso exited the race last month.
Candidates have until noon on Saturday, Feb. 7, to declare their intention to run for office. After filing, they must begin gathering signatures to qualify for the ballot.
Pratt rose to fame in 2007 when he began dating "The Hills" cast member Heidi Montag, and eventually became a regular on the series. The couple married the following year, and they have two children.
City News Service, Inc. contributed to this report.