Margo MacDonald was born in 1945 in Hamilton, Scotland and educated at Hamilton Academy, she trained as a teacher of physical education.

A committed and vocal Scottish nationalist, MacDonald won a shattering victory in the 1973 Govan by-election as a Scottish National Party (SNP) candidate, which had always been a Labour strong-hold. She failed to retain the seat in the February general election of 1974, but became Deputy Leader of the SNP in 1974 a post she would hold until 1979.

A naturally inclined left-winger, she was prominent in the socialist 79 Group and left the party in 1982 due this group's proscription.

She went on to establish herself as a forceful presenter of various radio and television programmes and she currently writes regular columns for Scottish newspapers including the Edinburgh Evening News and The Sunday Post.

By the mid-1990s she had returned to the SNP and in 1999, she was elected to the Scottish Parliament, representing the Lothians. This period marked her drifting from the leadership of the party, firstly under Alex Salmond and then John Swinney and she was placed fifth on the SNP list for Lothians for the 2003 Parliament election, whereas she had been first in 1999. This effectively ended her chances of being elected as a SNP MSP and she decided to stand as an independent.

MacDonald is viewed as being in the SNP Fundamentalist mould and in the party leadership election in 2000 she supported Alex Neil.

MacDonald is married to former politician and columnist Jim Sillars. She was re-elected as a MSP (as an independent) at the 2003 Scottish Parliament election.