Boston City Councilor Ayanna Pressley is challenging long-time incumbent Democratic Congressman Michael Capuano, launching what could be one of the state's most competitive — and closely watched — primaries this election cycle.

"Today I humbly announce my candidacy for the Democratic nomination in the 7th Congressional District," Pressley said in a statement. "This district and these times demand more than an ally, they demand an advocate and a champion."

Pressley, 43, was the first of woman of color elected to the city council in 2009. Capuano's district includes Somerville, where he lives and served as mayor, as well as Everett, Randolph, most of Boston and parts of Cambridge and Milton.

A Dorchester resident who was long rumored to be eyeing a run at Capuano's seat, Pressley vowed to be a "bold voice in Congress" if elected.

"Our country is facing a critical moment," she said. "While the cruel and dangerous tenor of the national political debate is new, the issues we are struggling to address — income inequality, systemic racism, and lack of economic opportunity — have dogged our nation for years. We have not yet delivered on our nation’s foundational promise of equality."

Capuano first won his seat in 1998 and has emerged as one of the delegation's most progressive members.