Eight of his shadow ministers and two parliamentary private secretaries have either resigned or have been sacked after defying the party whip by backing the motion put forward by the SNP.
Comment: Note that Starmer had openly threatened his party earlier on in the week that if they voted for an immediate ceasefire he would sack them - that's democracy in the UK.
Among the most high profile resignations was domestic violence and safeguarding secretary Jess Phillips, who said she was leaving the the Shadow Cabinet with a "heavy heart".
MPs voted 290 to 183, a majority of 107, to reject Labour's King's Speech amendment calling for longer "humanitarian pauses" - as opposed to a longer lasting ceasefire in Gaza.
The SNP's King's Speech amendment calling for "all parties to agree to an immediate ceasefire" in the enclave was also rejected 293 to 125.
Currently, the following MPs have either resigned or been asked to step down from their posts in the Labour party:
- Jess Phillips, shadow minister for domestic violence and MP for Birmingham Yardley
- Yasmin Qureshi, shadow women and equalities minister and MP for Bolton South East
- Afzal Khan, shadow business minister and MP for Manchester Gorton
- Paula Barker, shadow minister for devolution and MP for Liverpool Wavertree
- Rachel Hopkins, shadow minister for defence and MP for Luton South
- Sarah Owen, shadow minister for housing and MP for Luton North
- Naz Shah, shadow minister for crime reduction and MP for Bradford West
- Andy Slaughter, shadow solicitor general and MP for Hammersmith
- Dan Carden, parliamentary private secretary and MP for Liverpool Walton
- Mary Foy, parliamentary private secretary and MP for City of Durham
Starmer said he regretted that party colleagues had not backed his position.
"Alongside leaders around the world, I have called throughout for adherence to international law, for humanitarian pauses to allow access for aid, food, water, utilities and medicine, and have expressed our concerns at the scale of civilian casualties.
"Much more needs to be done in this regard to ease the humanitarian crisis that is unfolding in Gaza.
"And in addition to addressing the present, every leader has a duty not to go back to a failed strategy of containment and neglect, but to forge a better and more secure future for both Palestinians and Israelis.
"I regret that some colleagues felt unable to support the position tonight. But I wanted to be clear about where I stood, and where I will stand."
Sir Keir had met with some of his frontbenchers on Wednesday afternoon in a bid to persuade them to back the Labour's amendment instead.
A Labour spokesman said: "This is a whipped vote and every MP knows what the consequence of that means."
Comment: Twitter is ablaze with constituents calling out their MP for failing to vote for their to be an immediate ceasefire. Meanwhile the UK military has wasted little time in showing its support for Israel's genocide in Gaza, both in sending warships, spy planes, weapons, and troops to the region: UK's elite forces training in Lebanon, US Embassy in Beirut becomes new regional intelligence HQ
The spokesman acknowledged that shadow ministers had been given some freedom to speak in favour of a ceasefire, but said a Commons vote was a different matter.
"There is an understanding that there is a difference when it comes to the space that we have allowed, given that we fully understand that this is a very challenging subject... in the debate that there has been up to this point, but at the point at which there is a vote in Parliament that clearly is something that has a significance to it that everybody understands," the spokesman said.
The Middle East conflict has caused splits in the Labour Party, with the leadership backing the Conservative government's position of pushing for "humanitarian pauses" in the Israel-Hamas fighting.
However, several shadow ministers have openly called for a ceasefire instead.
On Wednesday, protesters were removed from the Commons, after holding up "ceasefire now" signs during the King's Speech debate involving shadow home secretary Yvette Cooper.
A group of five or six people stood up and held aloft the messages as Ms Cooper turned to the Israel-Hamas conflict in her speech. Environmental group Extinction Rebellion have since claimed responsibility for the protest.
Comment: The ruling Conservative government isn't faring much better, with 3 Prime Ministers in 2 years, and, in just the last few days the sacking on a top minister, alongside the reappointment of the widely despised former PM David Cameron.
Is it any wonder the UK is in the dire state that it's in?