Brad Lander, the outgoing comptroller of New York City and a former candidate for mayor, announced on Wednesday that he is running for the US Congress in a challenge from the left to fellow Democrat and representative, Dan Goldman – with the backing of the city’s progressive mayor-elect.

Lander will run in the Democratic primary contest next year for a liberal district in lower Manhattan and northwest Brooklyn.

He has received the blessing of New York’s mayor-elect Zohran Mamdani, whom he at first ran against and then supported as Mamdani soared ahead of establishment figures in that race, then won in November.

Lander shot to national prominence last June when he was arrested by masked federal officers while visiting an immigration court in New York, where he had turned up to protest and witness after incidents of people being snatched and detained by federal immigration enforcement officers.

Lander was accompanying a person out of a courtroom after an immigration hearing when he was grabbed and manhandled by officers and later detained by Immigration and Customs Enforcement (ICE).

New York City comptroller, Brad Lander, is placed under arrest by Immigration and Customs Enforcement (ICE) and FBI agents outside federal immigration court on 17 June 2025, in New York. Photograph: Olga Fedorova/AP

New York governor Kathy Hochul ended up intervening and Lander was released, although the authorities claim Lander assaulted officers, and the legal case is still playing out in court. Lander has been sharply critical of the Trump administration.

Launching his campaign, Lander said: “At a moment of dark oppression, we can shine by fighting back together.”

In a video, he added: “While the oligarchy drives an affordability crisis, they shouldn’t be able to buy a seat in Congress. While our immigrant neighbors are being demonized and attacked, we can put our bodies on the line to protect them.”

He also evoked the late children’s TV host Fred Rogers in his video, singing “Would you be mine? Could you be mine? Won’t you be my neighbor?”

In his endorsement, Mamdani praised Lander’s “unwavering principles, deep knowledge, and sincere empathy”.

Zohran Mamdani embraces Brad Lander after winning the Democratic primary for mayor at an election night watch party in Long Island City, New York, on 25 June 2025. Photograph: Julius Constantine Motal/The Guardian

Goldman is a former prosecutor who has also been a vocal critic of the federal government’s anti-immigration agenda and introduced legislation this month with some fellow congressional Democrats aiming to boost immigrants’ rights to appear in immigration court without risk of being targeted for arrest by ICE afterwards.

Goldman is a two-term congressman and heir to the Levi Strauss denim fortune, who acted as lead counsel for Trump’s first impeachment. He is considered a moderate Democrat, though he has supported raising taxes on wealthy people as well as the Green New Deal climate change proposal.

Bernie Sanders, US senator of Vermont, also endorsed Lander, calling him “a relentless fighter for working people”.

The Associated Press has requested comment from Goldman’s office.

Reuters and the Associated Press contributed reporting.