Six MPs have defected to the party in recent weeks, including former Tory MP Philip Lee, and ex-Labour MPs Luciana Berger and Chuka Umunna.
Mr Gyimah was one of the 21 Tories who had the Conservative whip removed after rebelling against Boris Johnson in a bid to prevent a no-deal Brexit.
Last December, the East Surrey MP quit as science and universities minister in a row over Theresa May’s Brexit deal.
The 43-year-old briefly stood in the race to become Conservative Party leader after Mrs May quit.
The Lib Dems currently have 18 MPs, having been boosted by a victory in the Brecon and Radnorshire by-election and the defections.
In an interview with the Observer, Mr Gyimah said he was “an outcast in the Conservative party”, adding: “But that’s Brexit. It has divided families. The country is divided. This is a huge fault line.”\
BREAKING: absolutely delighted to see @SamGyimah join the @LibDems today – just unveiled by @joswinson at #LibDemConf just now. He is a superb addition to the UK’s biggest and strongest #Remain party! pic.twitter.com/rM2TyY7EO6
— Chuka Umunna (@ChukaUmunna) September 14, 2019
He said: “I’ve been involved in the Conservative party for two decades. I’ve fought for the party. I have an unusual background – I’m not your typical Tory recruit.
“I’ve spent a long time evangelising about why people should look at the Conservative party seriously. It is sad that I find myself at a crossroads.”
