He was aged 75.
The Foyle MLA said that Cooper embodied the contrasting traditions of this island but that his driving ambition was to deliver civil rights, equality and fairness for people regardless of their background.
He said: “Ivan Cooper was born to break the mould.
“A working class Protestant man who saw a common injustice and inequality that had taken root in Protestant and Catholic communities, he dedicated his life to fighting it.
“As an early leader in the Civil Rights Movement, few have contributed as much to peace and equality on this island than Ivan.
“Organising marches in Derry for the right to a home, the right to a job and the right to a vote, Ivan often put himself in the path of danger to secure justice for people in every community.
“And on many occasions that meant that he suffered vilification and violence for his convictions. It never stopped him.
“Alongside his close friend John Hume, he helped blaze the trail on the path that led to the Good Friday Agreement.
“Anyone who knew Ivan knows that his selfless passion for justice continued to burn brightly into his later years.
“His unwavering belief that people on this island should come together to fight for common ideals and in their common interest is a lesson for us all. Especially as we face political division today.
“A man of sharp contrasts, sharp intellect and, it must be said, sharp tongue, he stands as a giant in the story of this island.
“And he holds a special place in the hearts of SDLP members.
“I want to express my deepest sympathies to Ivan’s wife Frances, his daughters Sinead and Bronagh and his entire family circle at this difficult time,” added Mr Eastwood.