Enjoying the patronage of Captain Hon. Samuel Barrington, Simonton saw early service aboard the Achilles 60 with that officer, from which ship he was commissioned lieutenant on 27 June 1759 and appointed to the Duke 90, Captain Samuel Graves. During the latter part of 1767 he was aboard the Tamar 16 at Plymouth, which vessel had of late been commanded by Captain Henry l’Anson. He later rejoined Captain Barrington, serving aboard the Portsmouth guardship Albion 74 in the spring of 1771.
During the summer of 1775 he was appointed to the storeship Maria in the Downs, being sent out to Virginia from Spithead later that year with ammunition and arms, and with orders to place himself under the command of Captain Henry Bellew of the Liverpool 28. The colonial governor of Virginia, the Earl of Dunmore, appointed him to the Dunmore 22 in December and he retained her until August 1776 whilst continuing as an agent of transports. He was also appointed agent of transports going out to Jamaica in the same year but in November was diverted to the Prince of Wales 74, which was being recommissioned in England by his patron, Captain Barrington.
By 1778 he was the senior lieutenant of what was now Rear-Admiral Hon. Samuel Barrington’s flagship Prince of Wales 74, Captain Benjamin Hill. He was promoted commander of the sloop Alderney 10 at Yarmouth on 5 May 1778 as a beneficiary of their Majesties Fleet review, and was posted captain on 9 July 1778.
Simonton was next appointed flag-captain to Rear-Admiral Sir Edward Hughes, recommissioning the Superb 74 and leaving England for the East Indies in March 1779. In 1780 he removed to the Sartine 32 in succession to the late Captain Alexander M’Coy, but she was lost on 26 November 1780 after hitting rocks during an attack on Hyder Ali’s ships at Calicut, Simonton having previously complained of being ordered to operate too close inshore.
After returning home he joined the Panther 60 in the Downs in May 1782 in place of the sickly Captain Thomas Piercy being employed in the Channel Fleet campaign of April-August, and seeing duty briefly as the flag-captain of Vice-Admiral Francis William Drake. After retaking the cutter Pygmy on 23 July he served at the relief of Gibraltar on 18 October. In the subsequent action off Cape Spartel his ship suffered several casualties. During 1783 he was the flag-captain of Vice-Admiral Mark Milbanke at Plymouth whilst continuing aboard the Panther, prior to her being paid off.
With his frequent applications for further service falling on deaf ears, Simonton became a superannuated admiral living at Greenwich, and he died in the early part of 1797.
He was regarded as an excellent officer.