Communist. Born in the manse in Half Morton (Dumfries and Galloway), Eaglesham was the son of the Free Church minister. He dropped out of the University of Edinburgh and, influenced by the radical socialist John MacLean (1879 - 1923), became a founder-member of the British Communist Party at the age of 18.
He travelled to Australia where he began to organise workers but was soon deported. Arriving in New Zealand, he became Secretary General of the fledgling New Zealand Communist Party and promoted the party amongst hard-pressed miners. He arrived in Moscow in 1930 and attended the Lenin School to study revolutionary philosophies, leaving in 1934 just before the Stalinist purges.
Suffering from tuberculosis, Eaglesham died in Stobhill Hospital and was buried in an unmarked grave at the Western Necropolis, Lambhill.