Mawson was born in Nether Wyresdale, Lancashire, and left school at age 12. His father, who died in 1877, was a warper in a cotton mill and later started a building business.
Mawson died at Applegarth, Hest Bank, near Lancaster, Lancashire, aged 72, and is buried in Bowness Cemetery within a few miles of some of his best gardens and overlooking Windermere.