Labour MP Imran Hussain has quit Sir Keir Starmer's shadow ministerial team over his desire to "strongly advocate for a ceasefire" in Gaza.
Mr Hussain was the shadow minister for the New Deal for Working People.
He said he remained committed to Labour's agenda but that his view on Gaza differed "substantially" from the position Sir Keir has adopted.
Sir Keir has called for humanitarian pauses in Gaza but has not supported calls for a ceasefire at this time.
In a resignation posted on social media, Mr Hussain said he wanted to be a "strong advocate" for a ceasefire alongside the UN and multiple charities, calling it "essential to ending the bloodshed".
"It is clear that I cannot sufficiently, in all good conscience, do this from the frontbench given its current position," he said.
He said he had "unequivocally condemned" Hamas's attack on 7 October and believed that "every country has the right to defend itself", but that that should "never become a right to deliberately violate international law on protecting civilians or to commit war crimes".
"It has always been my view, which I've made clear repeatedly in Parliament, that human rights are universal and that it is our duty to call out all those who violate international law," he said.
He went on to describe the situation in Gaza as "beyond that of a humanitarian catastrophe" and said a ceasefire would help both the passage of aid into the territory and the safe return of Israeli hostages.
He also said he was "deeply troubled" by an LBC interview Sir Keir gave on 11 October about Israel's actions in Gaza and that, while he appreciated Sir Keir's later clarification of the comments, he believed the party "needs to go further and call for a ceasefire".
In the interview, Sir Keir was asked whether it was "appropriate" for Israel to cut off the supply of power and water to Gaza.
"I think that Israel does have that right," he said. "Obviously everything should be done within international law, but I don't want to step away from the core principles that Israel has a right to defend herself."
A spokesman for the Labour leader later said he had only meant to say Israel had a general right to self-defence.
More than 60 MPs and at least 250 councillors have now backed calls for a ceasefire in the territory, but Sir Keir has argued that backing the move would not be the "correct position" at the moment.
In a speech last week, he said a ceasefire would leave Hamas's infrastructure intact, allowing them to carry out future attacks, and that calling for a humanitarian pause to allow aid into Gaza was "the only credible approach".
Mr Hussain was elected to represent the Bradford East constituency in 2015 and had been shadow minister for the New Deal for Working People since September.
He has previously served as shadow minister for work, shadow minister for justice, and shadow minister for international development.
Labour has been approached for comment.