Thomson was the first settler in the area known as Belmont, a suburb of Geelong and called his homestead Kardinia, a property now listed on the Register of the National Estate.

He was educated at Dr Todd's school in Tichfield, Aberdeen University, and in London, where he studied under Sir Everard Home and qualified for the medical profession.

He came over as medical officer and catechist for the Port Phillip Association, and built a house near the corner of Flinders and Elizabeth streets, Melbourne.

In May he acted as one of three arbitrators in connexion with disputes between Henry Batman and John Pascoe Fawkner, and before his house was completed he held service on Sundays in his tent.

Thomson was secretary to the first public meeting held in Melbourne, on 1 June; in October William Lonsdale appointed him medical officer at a salary of £200 a year.

He had been elected a member of the New South Wales Legislative Council as one of the representatives of the Electoral district of Port Phillip in 1843, but as it was difficult to attend the meetings at Sydney, soon resigned.

In the meanwhile, Thomson had resigned his seat in the council,[6] and visited England where he found he could get no information about the Australian colonies bills.

[5] His many activities had led to the neglect of his own financial affairs, and towards the end of his life he accepted the position of medical officer to the Sunbury boys' home.