The shadow secretary of state for Northern Ireland Vernon Coaker has joined seven other members of the shadow cabinet and resigned.
The resignations follow the sacking of shadow foreign secretary Hilary Benn overnight.
He has released a statement saying he believes it is "time for the party to unite behind a new leader" and serve as an "effective opposition".
He adds: "I have sought to make it my priority to provide reassurance to the people and political parties of Northern Ireland that Labour remains committed to the principle of consent, as expressed through the Good Friday Agreement and subsequent agreements.
"I know my successor in this role continues this vital work."
The leader of the UK's biggest trade union has said the country is 'riven' as a result of the EU referendum.
Len McCluskey told ITV News that the trade unions can help broker a peace deal and reunite the party now the "coup has failed".
Labour leader Jeremy Corbyn said he would 'reach out' to MPs that oppose his leadership but said they should 'respect democracy'.