British Conservative MP Stephen Phillips has resigned with immediate effect as a result of "irreconcilable policy differences" with Prime Minister Theresa May's government.
The differences are believed to be over Brexit policy.
"It has become clear to me over the last few months that my growing and very significant policy differences with the current government mean that I am unable properly to represent the people who elected me," he said in a statement on Friday.
No further details of his reason for leaving were given in his statement but last month the pro-Brexit Mr Phillips, a barrister and MP from Lincolnshire attacked Ms May's handling of the Brexit process.
In an article in the Guardian Mr Phillips, who had voted in favour of leaving the European Union in Britain's June 23 referendum, said May's government had lurched to the right in the absence of any centrist opposition.
"The latest feature of the current direction of travel is the government's desire not to seek the view of the House of Commons as to where its Brexit negotiations should end up," he wrote on October 11.
Ms May says she will invoke Article 50, the formal divorce announcement from the EU, by end-March 2017 but on Thursday the High Court ruled that a parliamentary vote was needed before she could do so. Ms May's aides say she will appeal the ruling.
She says the parliamentary vote requirement won't derail her timetable for Britain to leave the bloc.
Parliament is unlikely to defy the referendum vote by blocking Brexit, but if several lawmakers say it's likely the formal divorce won't be made by March.
The court ruling has spurred hope among investors and pro-EU lawmakers that parliament will now be able to put pressure on May's government - which has three high profile eurosceptic ministers in key roles - to soften any plans for a "hard Brexit", or a clean break with the EU's lucrative single market.
But it has enraged pro-Brexit campaigners and Britain's eurosceptic newspapers, with the Daily Mail calling the three judges who handed down the ruling "enemies of the people" and the Sun asking: "Who do EU think you are? Loaded foreign elite defy will of Brit voters."