Newsom obtained the papers from the Department of Elections in City Hall and paid a filing fee of about $2,500, both prerequisites of filing to run. The mayor has not officially announced a decision on whether he will run for the seat and has until Friday to file the papers.
Newsom, who in October dropped out the race for the governor's seat, has said he is intrigued by the idea of working on the state level, but that he is weighing a number of factors, including his new family.
A poll conducted earlier this year of 600 likely Democratic voters statewide showed Newsom receiving 33 percent of the vote if he ran for lieutenant governor, compared to 17 percent for Los Angeles City Councilwoman Janice Hahn and 15 percent for state Sen. Dean Florez from Kern County. The poll showed 35 percent of voters were undecided.
Both Hahn and Florez have declared their candidacy for the June primary. Candidates have until Friday to enter the primary.
If Newsom were to win the lieutenant governor's seat in the November election, he would remain mayor until taking the seat in January 2011. Board of Supervisors President David Chiu would then become mayor until the board, by a vote of six or greater, appointed an interim mayor.