Bonnar was born in 1871 and started his business career in Hong Kong at the Gibb, Livingston & Co. where he rose to the post of manager.
[2] Bonnar represented the chamber of commerce on the Legislative Council during the absence of Murray Stewart from the colony.
He was also a prominent member of the Royal Hong Kong Yacht Club and of the St. Andrew's Society, being the president in 1913 and 1914 and member of the general committee at the time he died.
[2] Bonnar was also president of the Hong Kong Football Club.
His son J. M. Bonnar was a well-known Colony Interport Rugby player.