He was a Labor Party member of the New South Wales Legislative Assembly from 1930 to 1932, representing the electorate of Waverley.
Clementson was born at Chippendale, and was educated to primary level before becoming a pastoral worker.
Clementson built his family home at 1 Want Street Mascot in 1918 and lived there until his death.
Clementson entered state politics amidst the landslide Labor win at the 1930 election, when he won the seat of Waverley, defeating Guy Arkins, the Nationalist MLA for abolished Rockdale.
His parliamentary career would be short-lived; he was easily defeated by United Australia Party candidate John Waddell at the 1932 election.