Councillor Iqbal Singh Padda, who has served as cabinet member for regeneration and growth in leader Kerrie Carmichael's ruling cabinet, said Labour had "taken the Asian vote for granted" in the borough.
He has represented the Labour stronghold of Greets Green and Lyng since 2018 but was deselected by the party last year.
He subsequently became one of four Asian councillors to protest against their deselections amid claims of racism against Labour's National Executive Committee.
It comes after former Labour councillor Sharon Davies was announced as a Conservative candidate for Langley in next month's poll.
In a parting shot, Councillor Padda slated the council for raising council tax by 4.99 per cent and "wasting" millions of pounds of taxpayers money on the Providence Place scheme in West Bromwich.
Councillor Padda said: "For too long Sandwell Labour have let residents down and taken the Asian vote for granted. Sandwell needs a new change.
"May’s elections provide a chance for all voters to send a message to Labour: that they’re fed up with council tax rises and poor services."
Councillor Carmichael said Mr Padda resigned on Saturday.
She added: "His decision to join the Conservatives has been made very quickly - it’s also a brave decision with the ongoing Conservative cost of living crisis.
"I wish him well and understand his disappointment with not being selected by the Labour Party this year."
In last May's elections the Conservatives gained nine seats, their first in the borough since 2015.
They gained a further seat in the Tividale by-election in July, but lost one earlier this year when Wednesbury South councillor Ian Chambers defected to Labour.
Voters will head to the polls on May 5.