He was a law professor and was jailed by a military junta in 1969-1972. In 1974 he participated in a national unity government. In 1980 he joined PASOK and in 1982 took over the justice ministry portfolio.
President Karolos Papoulias extended his condolences to the family of Mangakis.
"He was a charismatic jurist, a passionate fighter of democracy, an inspired politician who was distinguished for his honesty, dignity, sensitivity on issues of rights and freedoms," Papoulias said.