Managing director of Fairfield Shipbuilding and Engineering Co.
c1878 worked for John Elder and Co, and in 1885 made a partner.
1886, The firm was formed into Fairfield Shipbuilding and Engineering Co, Barnwell was made the Managing Director.
He was an active member of the Masons and a member of the Grand Lodge in Scotland. At one time he became Deputy Provincial Grand Master for Glasgow.
1898 Died aged 49 at Balfrom, near Glasgow.
Read his short obituary in The Engineer 1898/03/11.