Michelle Wu, a progressive, mounts a challenge to Boston’s mayor.

Michelle Wu, a 35-year-old Taiwanese-American city councilor and progressive Democrat, announced on Tuesday that she would enter the 2021 Boston mayoral race, asserting a moment of change for a city that has been led by white men since its incorporation in 1822.

Ms. Wu is challenging Mayor Marty Walsh, who is expected to run for a third term and has won widespread approval for his handling of the coronavirus.

It is difficult to defeat a sitting mayor in Boston; the last time it happened was in 1949. But , Massachusetts politics has been jolted repeatedly in recent years by progressive candidates who built come-from-behind campaigns around climate change and social justice.

Ms. Wu, a policy wonk and former student of Senator Elizabeth Warren, has proposed sweeping solutions to issues like gentrification and social inequality.