The ex-Conservative MP made public her new allegiance on X, formerly Twitter, following Labour leader Keir Starmer’s party conference speech.
She wrote: “I will be voting #Labour.
“With @Keir_Starmer as leader they have the values and competence to deliver the change our country desperately needs.”
Her post also included a cutting of a Times newspaper story on Starmer’s Tuesday speech, and underlined in red marker a section where the Labour leader suggests his party now embodies traditional Tory values.
Soubry helped found the Independent Group for Change, later Change UK, in 2019 after quitting the Conservative Party over then-prime minister Theresa May’s handling of Brexit.
Change UK, a group of disaffected Labour and Tory MPs, disbanded after they all lost their seats in the 2019 election.
The barrister and journalist has been a Tory minister in the business department and the Ministry of Defence.