Labour MP Ashok Kumar, who was found dead in his home, died from natural causes, police said today.
The body of the 53-year-old was discovered yesterday afternoon after his staff were unable to reach him by telephone and raised the alarm.
Cleveland Police said that following a post mortem examination the Middlesbrough South and East Cleveland MP's death was from natural causes.
Prime Minister Gordon Brown, and his immediate predecessor Tony Blair, led tributes to Mr Kumar.
The Prime Minister said he was "greatly saddened" after hearing the news.
"Ashok was a hard-working constituency MP who took pride in representing the people of Middlesbrough as both a councillor and MP," Mr Brown said.
"He was a tenacious campaigner for his constituents and a warm and incredibly generous man. His long-standing campaigns to keep shipbuilding in Teesside were respected by all sides of the House."
Mr Blair, who was a fellow North East MP until he stood down from Parliament in 2007, described his loss as "a genuine tragedy and source of real sadness".
"Ashok was a dedicated and committed local Member of Parliament, representing Middlesbrough with a real passion and determination to serve the community he was from," he said.
"As a neighbouring MP I saw first hand his commitment to the North East where the support he received grew year after year."
Born in India, Dr Kumar worked as a research scientist for British Steel before being elected as an MP in 1991, when he won a by-election for the Langbaurgh seat.
His first spell in Parliament proved to be short lived when he lost the seat in the 1992 general election, but he was re-elected in 1997 to the newly created Middlesbrough South and East Cleveland constituency.
Dr Kumar, who was single, was a Commons aide to Environment Secretary Hilary Benn, who said he was "deeply shocked and saddened".
A Cleveland Police spokeswoman said: "A post-mortem was carried out this morning and revealed that the 53-year-old died from natural causes."
Sean Price, chief constable of Cleveland Police, added: "Ashok Kumar was a talented MP who was dedicated to serving his constituents, and was always greatly supportive of Cleveland Police.
"I was extremely saddened to hear the news of his death and my thoughts are with his family and friends."