Of an ancient Northumbrian family, Forster was the co-heir of his maternal uncle, Ferdinand Forster, M.P., of Bamburgh Castle, whose branch of the family represented Northumberland from 1689 till his murder in 1701. Returned for the county as a high church Tory in succession to his father in 1708, he continued to represent it till his expulsion from the House of Commons for participating in the rebellion of 1715.
On 21 Sept. 1715 Forster, then in London, was one of six Members whose arrest was ordered on a charge of being ‘engaged in a design to support the intended invasion of the kingdom’.
Taken to London with the other chief rebels, Forster was imprisoned in Newgate, from which he escaped a few days before the day fixed for his trial. The Government issued a description of him as ‘one of middle-stature, inclined to be fat, well-shaped, except that he stoops in the shoulders, fair complexioned, his mouth wide, his nose pretty large, his eyes grey, speaks the northern dialect’, and placed a reward of £1,000 upon his head.
I have convinced Mr. Forster that it is reasonable for him not to think of leaving this place at least for some time. He is a mighty honest good man, and I am very glad to have him here and shall endeavour to make him as easy as I can as to money matters.
When the Pretender moved to Avignon from Rome he summoned Forster (16 Oct. 1727) to join him:
You see honest Tom I am as good as my word, I have no sooner fixed my habitation here, but I send for you.
As Forster had been excepted from the Act of Indemnity, his brother John succeeded to Adderstone in 1725. Thereafter, he corresponded with the next heir, his nephew Thomas, who held out ‘little hopes’ of his ‘getting anything from the succession’. In October 1738 he died at Boulogne, in France, awaiting news from his nephew.
