Walker was found guilty in 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.
The disgraced ex-politician was freed from Dumfries Prison today under automatic early release rules.
He made no comment as he walked out of the jail at 8.10am and into a waiting silver car which drove him away.
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. On various occasions, Mrs Gruber was punched, slapped, kicked and pushed to the ground. He also breached the peace by leaping into her home brandishing an air rifle.
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, three of which involved slapping or punching her on the face. 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.
He resigned after facing intense pressure from campaigners and MSPs to step down from the Scottish Parliament following his conviction.
Walker, who denied all the charges, plans to appeal against his conviction and has a court hearing scheduled for next month.