Robert Lyndon Day (10 May 1886 – 16 July 1968) was an Australian politician.
He was born in Melbourne to compositor George Day and Mary Ann Campbell.
He was educated at Preston and Northcote and was an apprentice sailor by the age of thirteen.
He deserted his ship in the United States, and five years later returned to Australia, becoming a canecutter in Cairns.
From 1953 to 1967 he was a Labor member of the New South Wales Legislative Council.