Macdonald studied at the Glasgow Academy and University of Glasgow before undertaking National Service[1] He joined the Scottish National Party (SNP), and began working on a farm in Killearn, in 1956 starting a branch of the SNP in nearby Balfron.
The following year, he inherited the family farm in Newmilns, and started the Irvine Valley branch of the party.
Supported by election agent Alan Niven, Macdonald won 18.7% of the vote in a seat which the party had never previously contested.
This result delighted Macdonald, who sold the farm to become the SNP's first full-time national organiser since the early 1950s.
He also stood unsuccessfully for the SNP in several elections: Clackmannan and Eastern Stirlingshire in 1970, Hamilton in February and October 1974, when he took 39% of the vote, and Central Ayrshire in 1979.