Pepper was an official war artist during World War II.
He married artist Kathleen Daly in 1929.
The couple visited the eastern Arctic in 1960 to study Inuit art.
Pepper taught at the Ontario College of Art and the Banff School of Fine Arts.
He was a founding member of the Canadian Group of Painters in 1933.
In 1957, he was named to the Royal Canadian Academy of Arts.
In 1954 he was one of eighteen Canadian artists commissioned by the Canadian Pacific Railway to paint a mural for the interior of one of the new Park cars entering service on the new Canadian transcontinental train.