Mason was born at Kennoway in the Kingdom of Fife.
[1] By 1889 he is recorded as being a member of the London Board and managing director of the English and Australian Mortgage Bank Ltd[2] He was also a Justice of the peace in Glasgow.
[3] His son, David Marshall Mason was an MP, being Liberal member for Coventry from 1910–1918 and Edinburgh East 1931–35[4] Mason was elected as a Liberal Member of Parliament for Mid Lanarkshire in the 1885 general election defeating his Conservative opponent by 296 votes.
At the 1886 election Mason held his seat with an increased majority 870, this time against Liberal Unionist opposition and emphasising his support of Irish Home Rule.
[6] Having previously been in what appeared to be good health, Mason died suddenly of heart disease at his London home in Streatham Hill on 21 April 1890.