Thomas Gregson was educated in Edinburgh and migrated to Van Diemen's Land, (later renamed Tasmania) in 1821 with his wife as the result of the family differences.

Gregson was made a magistrate and in 1825 was assisting Andrew Bent in his conflict with Governor Arthur for the liberty of the press.

In July 1842 Gregson became a member of the Tasmanian Legislative Council, and three years later led the opposition to the governor, Sir Eardley-Wilmot, in his attempt to raise the import duties.

But he was found to be unsuitable for his office; he lacked moderation, self-control and tact, and his government was defeated about eight weeks later.

Gregson was particularly important as a reformer in his early days, fighting for the liberty of the press, for trial by jury, and the abolishment of penal transportation.