Ulster Unionist Peer, Lord Empey, said:
“I worked with Seamus Mallon throughout the Mitchell Talks process, and indeed served as Acting First Minister briefly while he was deputy First Minister.
“There was no doubt that, if John Hume was the SDLP's ideas man, Seamus was the person to turn those ideas into practice and workable solutions.
“Seamus was emotional at times, but a steadfast opponent of all forms of paramilitary violence. He could see what damage it was doing to his dream of a genuinely united Ireland.
“I don't believe the Good Friday process could have succeeded without him. He understood the practicalities and realities of politics and government, something that some of his colleagues failed to appreciate.
“He also had a dry sense of humour, especially during the many crisis talks we had at Hillsborough and other locations over the years.
“He always felt let down by both Governments for their failure to uphold both the letter and spirit of the Agreement and was furious at times when deals were done behind our backs.
“I think all of us have lost a champion of democracy and justice today.”