Tonken was commissioned lieutenant on 6 April 1757, and in that rank served aboard the Portsmouth guardship Achilles 60, Captain Hon. John Luttrell, from December 1766 until March 1767, and the Chatham guardship Ramillies 74, Captain Richard Edwards, from 1768-70. In 1773 he was the first lieutenant of the Sheerness guardship Triumph 74, Captain Hon. George Falconer, and in June 1775 he rejoined that officer as first lieutenant of the guardship Mars 74 at Chatham, remaining with her until the following summer.
Having gone out to North America as an agent for transports he succeeded Captain John Bourmaster as the Principal Agent for Transports at New York when that officer was posted captain on 9 September 1777. As a reward for his services on the North American station he was promoted commander of the Otter 14 for purposes of rank, and for one day only, on 25 December 1778.
In December 1779 Tonken joined the Charleston expedition as the principal agent for transports, enduring a difficult passage south in which he had to supervise the removal of troops, women and children from sinking transports. Ashore he assisted Captain Hon. George Keith Elphinstone in conveying the army across the Ashley River prior to the port s capitulation on 11 May. He was posted captain of the captured frigate Charleston for purposes of rank on 15 May, again for one day only, and he continued as the principal agent for transports on the North American station until coming home in 1782.
He commissioned the Sandwich 90 at the commencement of the Dutch Armament in October 1787 at the Nore for the flag of Rear-Admiral Richard Edwards and thereafter Rear-admiral John Dalrymple, and was also with the latter officer aboard the Dictator 64 on the same station from April 1791. He died of an attack of the palsy on 4 September whilst still commanding the Dictator, and he was buried at St. Mary Magdalene Church in Gillingham, Kent..
Tonken was survived by his wife, Anne, who died in November 1803, but was predeceased by two sons; William, who died on 18 July 1770 at the age of 12, and Thomas, who died on 14 November 1780 whilst serving as a naval lieutenant in the West Indies. He was also survived by a daughter, Catherine, who in 1788 had married a gentleman from the Pay Office at Chatham.
ell of the Emerald 32, who was much impressed with the younger officer.