Labour MP Ashok Kumar has died unexpectedly, his constituency office has announced.
The 53-year-old member for Middlesbrough South and East Cleveland was found at his constituency home in Middlesbrough on Monday morning.
A spokesman for his office confirmed his death, describing it as "sudden" and "accidental".
"Ashok was a first class constituency MP and a great friend. I, along with many people will sadly miss Ashok," the Northern Echo newspaper quoted Redcar and Cleveland borough council leader George Dunning as saying.
"Ashok worked tirelessly for his constituents. [he] was extremely disappointed at the recent job losses at Corus on Teesside. I am sure his former steel colleagues will miss Ashok who was a fantastic ambassador for Teesside Steel."
Mr Kumar's constituency is viewed as one of the most competitive in the Teesside area come the general election.
Although steelmaker Corus' Redcar plant is not in his seat, its totemic importance to the local economy means the issue is dominating politics in the run-up to polling day.
Dr Kumar entered parliament in 1991 and had served as MP for Middlesbrough South and East Cleveland since 1997.
He faced a tough challenge from Conservative candidate Paul Bristow, who today paid tribute to his opponent.
"I was shocked to hear of the sudden death of Ashok Kumar," Mr Bristow told politics.co.uk.
"I had the utmost respect for him. He fought passionately for the interest of Teesside and will be remembered as a fine MP with strong values and beliefs."
He added: "Ashok will be sorely missed and I send my sincere condolences to his family and friends."
Dr Kumar was a prominent "liberal humanist" in parliament who campaigned for a national holiday on the day of Charles Darwin's birth.
The British Humanist Association's chief executive Andrew Copson said: "The loss of Ashok's commitment, good humour and humanist outlook will felt by many in and outside of parliament."