As Harold Lever, he served as an MP in central Manchester for 34 years until 1979 when he was made a life peer. He was widely acknowledged to be a Labour paradox - a millionaire and financial expert who was a witty and erudite exponent of socialist-capitalist principles.
His expertise led him to become Chancellor of the Duchy of Lancaster in 1974 and Harold Wilson's financial adviser and negotiator of Britain's North Sea oil contracts.
Lord Lever went on to advise James Callaghan from 1976 until his defeat by Margaret Thatcher in the 1979 general election.
Born to a Jewish family in Manchester in 1914, Lord Lever's socialist beliefs never prevented him enjoying his wealth which he accrued as a lawyer and as a shrewd stock market investor.
On the right, pro-European wing of Labour, he was elected as shadow frontbench spokesman on european affairs when the party went into opposition in 1970. He resigned two years later, along with Roy Jenkins, over Labour's stance on joining the EEC.
He was re-elected to the shadow Cabinet later that year and went on to become Chancellor of the Duchy of Lancaster when Labour returned to power in 1974.
Although frequently under fire from left-wingers in the party who accused him of lacking commitment to socialism, Lord Lever insisted that he had been a radical throughout his life.
In a tribute, the Labour MP Gerald Kaufman, said: "Harold Lever was one of the most brilliant Members of Parliament the Labour Party has ever had. He had a dazzling brain and a superb wit."
Obituary, page 10