Earlier Wednesday, the Lib Dems' home affairs spokesman Brian Paddick, who is gay, announced his resignation "over concerns about the leader's views on various issues", referring to Farron's refusal to deny that he considered homosexuality a sin during the election campaign.
After the matter refused to go away and surfaced again during the election campaign, Mr Farron said it had felt "impossible" to be both Lib Dem leader and a Christian.
After days of facing questions, Mr Farron was forced to state that he did not believe gay sex was a "sin".
The party gained four seats, going from eight to 12 last week, but its vote share dropped.
Despite some successes, the campaign was criticised for focusing on a second European Union referendum and Farron's appearances were dominated by questions over his views on gay sex and later on abortion.
But he said he could no longer reconcile his strong Christian faith with his responsibilities as leader of a liberal party.
There are Christians in politics who take the view they should impose the tenets of their faith on society, but I have not taken that approach because I disagree with it.
Back in 2007, he told a magazine: "Abortion is wrong".
But there was discomfort within his party over his personal views, and even though membership doubled and there was a modest increase in Lib Dem MPs at last week's general election, his effectiveness was always going to be dogged by questions over his faith. "I've tried to answer with grace and patience".
Tim Farron has shockingly resigned as leader of the Liberal Democrats in the British Parliament. If there is more than one candidate, the position will be decided through a secret ballot after a hustings on June 27 or a single appointment will be made on June 20.
"Journalists have every right to ask what they see fit".
His resignation means that he follows Ukip's Paul Nuttall as the second party leader to resign in the wake of the election result.