Adrienne Adams, the City Council speaker vying to become the first female mayor of New York City, will announce two major endorsements on Wednesday that could provide momentum in the crowded race.

Ms. Adams will receive endorsements from Letitia James, the state attorney general, and from District Council 37, the city’s largest municipal union.

Ms. James, who is broadly popular among Democrats in New York, plans to appear with Ms. Adams at a campaign rally on Wednesday.

“Adrienne Adams is a fearless leader who puts people over politics,” Ms. James said in a statement. “She has repeatedly stood up for New Yorkers and won, keeping libraries open and protecting child care for families.”

Ms. James also praised Ms. Adams for “leading the city’s fight against the Trump administration,” including her opposition to allowing federal immigration authorities to open offices at the Rikers Island jail complex.

Ms. Adams entered the race later than the eight other major Democratic candidates in the June 24 primary, and she has yet to break through in public polling. The dual endorsements may aid her argument that she has the institutional support to defeat the current front-runner, former Gov. Andrew M. Cuomo.