Walker was found guilty last August of 23 assaults and one breach of the peace which spanned decades.
The 71-year-old, who clung to his Dunfermline seat for 16 days after the verdict, was jailed for a year at Edinburgh Sheriff Court last September.
Sheriff Kathrine Mackie, who heard the two-week trial, told Walker he had showed "contempt" for his victims as she imposed the maximum sentence available to the court.
Walker was freed from Dumfries Prison yesterday morning under automatic early release rules.
He made no comment as he walked out of the jail and into a waiting silver car.
Sheriff Mackie found Walker guilty of assaulting his first wife, Maureen Traquair, on three separate occasions in the 1960s and 1980s.
He was convicted of assaulting his second wife, Anne Gruber, 15 times between 1978 and 1984.
Walker was further found guilty of assaulting and injuring Mrs Gruber's 16-year-old daughter, Anne Louise Paterson, by repeatedly striking her on the head with a saucepan in 1978.
He was found guilty of four assaults on his third wife, Diana Walker.
The attacks happened between June 1988 and January 1995.
The former SNP MSP was suspended and later expelled from the party after the allegations surfaced in March 2012, and he stood for some time as an independent MSP.
Walker, who denied all the charges, plans to appeal against his conviction and has a court hearing scheduled for next month.