Mr Brown said: "John MacDougall gave more than 30 years of distinguished public service to Fife and he will be remembered as a true servant of the people.
"Over three decades, he has been a good personal friend of mine."
Mr MacDougall started work at the RGC oil rig construction yard at Methil, before union activism led him into politics.
The former boilermaker led Fife Council for nine years before taking over the Central Fife Westminster seat, held by Henry McLeish, who went on to become Scottish first minister.
Following boundary changes, Mr MacDougall stayed in parliament as MP for the new Glenrothes constituency, where his majority at the last election was 10,664.
Mr MacDougall was known for his extensive connections in the EU, having sat on the body which investigated financial irregularity in the European Community.
He also served as vice-president of the Assembly of the European Regions.
Mr MacDougall, who had been fighting Mesothelioma for two years, never fully recovered from surgery in London last year and had been chronically ill.
John MacDougall's life in politics
1947 - Born in Dunfermline, Fife
1964 - Starts work at Methil oil rig construction yard
1978 - Becomes trade union shop steward
1981 - Joins Labour Party, becoming chairman of local branch
1982 - Elected as Fife councillor and serves for nearly 20 years
2001 - Elected MP for Central Fife
2005 - Re-elected as MP for new Glenrothes seat
He has left behind his wife Cathy and two children, Scott and Julie.
SNP MP Angus Robertson said he was saddened by Mr MacDougall's death.
He added: "We may have been on opposite sides in the House of Commons, but John carried the respect of people right across the chamber and was passionate for the issues he believed in and the welfare of his constituents, which he cared about deeply."
North East Fife MP and former Liberal Democrat leader Sir Menzies Campbell, said: "His courageous fight against illness in recent times meant parliament was denied his shrewd interventions on so many issues."
Scottish Conservative MP David Mundell, said: "John was a kind and decent man who was dedicated to the service of the people of Fife, with distinguished service both in parliament and local government."
The last by-election fought in Fife, in February 2006, saw the Liberal Democrats overturn a Labour majority of more than 11,500 to win the seat of Dunfermline and West Fife.
And in a by-election last month, the SNP won what was thought to have been one of Labour's safest seats, Glasgow East.
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