Garrett Armstrong arrived on the Recovery as a soldier of the New South Wales Corps in 1808. The Recovery departed Rio at the beginning of May in company with the Lady Sinclair, however parted soon afterwards in a gale of wind. The Sydney Gazette reported that the Recovery arrived off Sydney Heads on Saturday 23rd July 1808 with 119 troops of the New South Wales Corps. Captain Cummings of the NSW Corps landed that same evening with the Naval Officers. The troops were reported to be in good health and spirits.
Garrett Armstrong was court-martialled for desertion in June 1809 
- At a General Court Martial held at Sydney on 16th June, of which Major Abbott of the New South Wales Corps was President, was tried Garrett Armstrong, Private Soldier in His majesty's New South Wales corps charged with having deserted from the said Corps, and not having returned until brought back by a Party; of which charge he was found Guilty and sentenced to be transported as a Felon, and to serve as a convict in NSW or its dependences during the Term of his natural Life.
In January 1810 he was released from Sydney Gaol on the occasion of Lachlan Macquarie taking over as Governor.
Sentence of Death Commuted
In June 1810 Garrett Armstrong was found guilty of forgery and received a sentence of death which was commuted. He was then sent to work in work gangs alongside other convicted criminals.
In November 1810 he absconded from the gaol gang in Sydney and the following March he absconded from Lane Cove after receiving and selling eight men's rations from the Public Store.
He was sent to Newcastle on the Lady Nelson in June 1811 just one month after notorious convict James Hardy Vaux. Other prisoners transported to Newcastle on the Lady Nelson on the same day as Garrett Armstrong included
William Gorman, Hannah Chapple and three women who were wives of soldiers of the 73rd who were being sent to Newcastle as punishment for poor behaviour.
By September 1811 Garrett Armstrong had absconded from Newcastle, this time with two notorious bolters John McCabe and John Fitzgerald. They were believed to be lurking about the lower Hawkesbury region and inhabitants were cautioned against harbouring or employing them on pain of prosecution. All three were soon apprehended and sent back to Newcastle.
He absconded again on 20th November 1812 with James Camm and William Harrison Craig. They were captured and punished with 25 lashes each. Lieutenant Skottowe was Commandant at the settlement at this time.
Lieutenant Thomas Thompson was Commandant when Garrett Armstrong absconded from Newcastle in March 1814. Armstrong was captured and sent back a week later.
Van Diemen's Land
In 1819, still a prisoner, he was sent to Van Diemen's Land on the Prince Leopold to work in public service. He was granted a Ticket of Leave in Hobart in 1835.
Garrett Armstrong died on 1st February 1836 at Launceston, Tasmania.
 A Ancestry.com. New South Wales, Australia, Colonial Secretary's Papers, 1788-1825 (1) Series: (NRS 936) Copies of letters sent to Van Diemen's Land, Newcastle and Norfolk Island, 1810-1813 Item: 4/3492 Page: 29