Months after finishing a distant third in her bid to become public advocate, former City Council Speaker Melissa Mark-Viverito is now planning for a run for Congress, sources told The Post.

Mark-Viverito is telling close confidantes that she plans to run in next June’s Democratic primary for a South Bronx congressional seat held by Rep. Jose Serrano, who is retiring in 2020 after being diagnosed with Parkinson’s disease. The seat represents one of the poorest districts in America.

The race is already stacked with candidates, including Bronx council members Ritchie Torres and Ruben Diaz Sr. and state Assemblyman Michael Blake.

Mark-Viverito served on the council from 2006 through 2017, including her final four years as speaker, when she came under fire for her relentless support of Puerto Rican nationalist Oscar Lopez Rivera, a convicted terrorist.

She serves as interim president of Latino Victory, a progressive political group.

Mark-Viverito’s name figured prominently in the downfall of Puerto Rico Gov. Ricardo Rossello. He apologized after it was revealed that he called her a “whore” in leaked text messages with aides.

Mark-Viverito was born in Puerto Rico and has deep ties to the island.

She did not immediately return messages.