The former justice secretary David Gauke is yet to decide whether to stand as an independent candidate in the general election.
Mr Gauke, who became the MP for South West Hertfordshire in 2005, had the Tory whip removed after he voted against Boris Johnson's Brexit deal.
The 48-year old former solicitor tweeted that he feels "regret" that he cannot continue as a Conservative.
He said he would reach a decision soon about standing as an independent.
Mr Gauke previously said a no-deal exit would be a "big mistake" for the UK and he would not be "complicit" in something which would see people lose their jobs.
My message to the members of South West Hertfordshire Conservative Association. pic.twitter.com/qfnCZkmpvo— David Gauke (@DavidGauke) November 8, 2019
On Twitter Mr Gauke said: "I appreciate that my views on Brexit do not accord with the majority in the modern Conservative Party and that our paths have diverged."
He said he would look back on his time as Conservative MP for South West Hertfordshire "with great fondness".
A number of people replied to his tweet asking if he would still consider standing in the general election, to which he replied: "Thanks for the messages about standing as an independent. Will reach a decision on that soon."
Some parties are yet to choose their candidates for South West Hertfordshire but Tom Pashby has been selected for the Green Party and Sally Symington will represent the Liberal Democrats.