The New York Working Families Party is enlisting Walton as a spokesperson and organizer.
Brown lost the Democratic primary to Walton, a democratic socialist, but defeated her with a write-in campaign in the general election.
The probable outcome is a remarkable reversal of fortune for Democratic nominee India Walton, who defeated the incumbent mayor in the primary.
But she faces an uphill battle against Mayor Byron Brown, who is running an unusually competitive write-in campaign in Buffalo, New York.
At a rally, the New York congresswoman also framed a Walton victory as important for American democracy.
India Walton, a progressive, won the Democratic primary, but centrist Mayor Byron Brown is challenging her via a write-in campaign.
Walton, a democratic socialist, defeated Buffalo, New York, Mayor Byron Brown in the Democratic primary, but Brown is running a well-funded write-in campaign.
Walton handily won the Democratic primary against the New York city's mayor, but Brown is launching a write-in campaign against her for the general election.
"People do not like being taken for granted," said the leader of a union that endorsed Walton.