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.
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. She currently sits as one of three independents elected to the Scottish Parliament.
MacDonald is married to former politician and columnist Jim Sillars.