The son of a Welsh miner Thomas Isaac, who later died in the mines, Jones rose up the ranks of the Labour Party to become Member of Parliament for Pontypridd in 1922.
He nonetheless managed to attend Ruskin College, Oxford, to study political and economic history for two years.
Mardy Jones began his political career as lecturer in south Wales for the Independent Labour Party.
In December 1930 Jones gave his wife and 12-year-old daughter a pair of Commons rail vouchers, which they were caught using.
Thomas Isaac Mardy Jones died on 26 August 1970, aged 91, at Harold Wood Hospital in Essex.