Labour shadow minister Jack Dromey has died at the age of 73, his family have announced.
Husband of fellow Labour MP Harriet Harman, with whom he had three children, Mr Dromey was a former deputy general secretary of the Transport and General Workers' Union and had been Labour Party treasurer.
He was elected to parliament in May 2010, representing Birmingham Erdington, and contributed to a Westminster Hall debate on Thursday.
He was also shadow minister for immigration.
His family said in a statement: "Jack Dromey MP died suddenly this morning aged 73 in his flat in Erdington. He was a much loved husband, father and grandfather, and he will be greatly missed."
His son, Joe Dromey, said he had "died suddenly", adding: "We loved him so, so much. Rest in peace big man x."
Mr Dromey was born to Irish parents in 1948 and grew up in Kilburn in London.
Labour leader Sir Keir Starmer said he "dedicated his life to standing up for working people".
He added: "From supporting the strike at the Grunwick film processing laboratory, when he met Harriet, through to being elected to represent Birmingham Erdington, Jack lived his commitment to social justice every day.
"He was highly respected and warmly regarded across parliament."
Commons Speaker Sir Lindsay Hoyle said Mr Dromey was a "life-force" and colleagues were "in disbelief" that he had died.
He continued: "I have known Jack since the mid-1980s when we fought to save the Royal Ordnance Factory in Chorley - he was national officer for the Transport and General Workers' Union and I was chair of economic development at Chorley Council.
"He was a great guy, down to earth, always positive and always looking to support and save jobs."
Former Labour prime minister Gordon Brown said he was "mourning the death of a friend, colleague and great humanitarian".
Mr Brown's predecessor Tony Blair said he was "shocked and greatly saddened by the news about Jack Dromey", adding: "I have known him for almost 40 years. He was a complete stalwart of the Labour and Trade Union movement, who dedicated his life to the service of others."
Culture Secretary Nadine Dorries said Mr Dromey was a "kind gentleman with no side or edge" and his "politics never stood in the way of his gentle nature".
Education Secretary Nadhim Zahawi said he was "shocked and heartbroken" and that Mr Dromey "was a friend".
Prime Minister Boris Johnson tweeted: "Deeply saddened to hear of the death of Jack Dromey.
"My thoughts are with Harriet and the family, and all those who knew him as a friend. May he rest in peace."