The former Labour politician said a “great oak has fallen in the sparser political forest with the passing of Mr Speirs” a former STUC general secretary who has died at the age of 57 after a long illness.
He also said regarded him as an “older, more sophisticated brother.”
Those who attended Renfrew Town Hall included First Minister Alex Salmond, Labour leader Ian Gray and former First Minister Jack McConnell.
The building was packed with former colleagues, fellow activists, relatives and well wishers forcing left-wing firebrand Tommy Sheridan and former Labour leader Wendy Alexander to stand on the pavement outside.
Mr Galloway told mourners: “In many distant parts of the world the passing of Bill Speirs is being noticed and mourned.
"There are people as far away as South Africa and Palestine and indeed many parts of the Arab world, former Yugoslavia, the former USSR, whose lives Bill touched and graced and improved who today are mourning his passing.
The Respectg MP, who saluted as the former union chief’s coffin passed by him in a hearse, added: "He was an eagle, a leader. I will never, ever, ever forget Bill Speirs and what he meant in my life, and I suspect I am not alone in that."
In his tribute, Mr McConnell said it was "a real honour" to be able to pay his respects to the trade unionist and that Scotland had lost a “special son.”
He said: "I am proud to have known Bill, and learned from him over the past 30 years. This past week, friends and colleagues have used a range of words to describe Bill Speirs: intellect, passion, humour, energy, motivated and motivating, internationalist, loyal friend, decent, charismatic.
"But his special contribution was in his belief that ordinary people, mobilised and organised, could effect change. Change for themselves and change in others.
"He believed that they could make an impact and have an influence on their community, their company or their country.
"Bill Speirs built bridges between people, not walls to keep people apart.
"He was never ending in his passionate belief that Scotland would be a better more democratic place, a more just society, with a Scottish Parliament in place. Now it is here but he is gone.
"Scotland lost a special son last week. We all lost a special friend. We will miss him and his huge contribution to our national life.”,
The former leader added that mourners were there to remember his “immense contribution, his fun, his intellect, his style, his inspiration, and his values of decency, compassion and respect."
Mr Speirs joined the STUC as an assistant secretary in 1979. He became deputy general secretary in 1988 and general secretary 10 years later.
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