Labour MP Jack Dromey died suddenly in his flat in Birmingham on Friday, the shadow minister’s family said.
The father-of-three, who was married to party grandee Harriet Harman, is understood to have died from natural causes.
The 73-year-old had represented Birmingham Erdington since 2010 and contributed to a Parliament debate as recently as Thursday.
A statement issued by the Labour Party on behalf of Mr Dromey’s family said: “Jack Dromey MP died suddenly this morning aged 73 in his flat in Erdington.
“He had been a dedicated Member of Parliament for Birmingham Erdington since 2010.
“He was a much loved husband, father and grandfather, and he will be greatly missed.”
Mr Dromey and Ms Harman’s son Joe tweeted: “Our dad – Jack – died suddenly today.
“We loved him so, so much.
“Rest in peace big man x.”
Ms Harman, who served as deputy Labour leader between 2007 and 2015, announced last month that she will not run for her Camberwell and Peckham seat in the next general election.
Labour leader Sir Keir Starmer said: “The proud son of Irish parents, Jack Dromey dedicated his life to standing up for working people through the Labour movement, becoming deputy general secretary of the UK’s largest trade union and then a Labour MP.
“From supporting the strike at the Grunwick film processing laboratory, when he met Harriet, through to being elected to represent Birmingham Erdington in 2010, Jack lived his commitment to social justice every day.
“Jack was recognised for his determination to stand up for his constituents and he was highly respected and warmly regarded across Parliament.
“My thoughts and those of the whole Labour movement are with Harriet, their children and all those who knew and loved Jack.”
Tributes pour in for ‘legend’ MP
Liam Byrne, Mr Dromey’s Birmingham colleague and MP for Hodge Hill in the city, said: “Stunned and in shock.
“It was a privilege of my life to work hand in glove with Jack in the West Midlands for the last decade and he chaired my Mayoral campaign brilliantly.
“We’ve lost a legend. But his legend will live on. In the countless he changed for the better.