The MPs are Jonathan Gullis, who represented Stoke-on-Trent North, Lia Nici, formerly Grimsby MP, and Chris Green, the former Bolton West Tory MP.
Mr Gullis, a former Conservative Party deputy chairman and education minister, told the BBC he believes the party has “lost touch with the people it was meant to serve”.
The defections are the first since Danny Kruger, the sitting MP for East Wiltshire, left the Conservatives for Reform in September.
A Reform party source claimed the Conservative Party is “dead” and said that only Reform can defeat Labour in the next election.