Suckling joined the Royal Navy in 1739 and saw service in the English Channel and Mediterranean Sea during the War of the Austrian Succession.

With the support of relatives including Prime Minister Sir Robert Walpole, Suckling was promoted quickly and received his first command in 1754.

There he played a major part in the Battle of Cap-Français in 1757 and fought an inconclusive skirmish against the French ship Palmier in 1758 before returning to Britain in 1760.

Suckling was employed in the aftermath of the Capture of Belle Île in 1761 destroying French fortifications on the Île-d'Aix and went on half pay at the end of the war in 1763.

Suckling continued throughout the period to assiduously attend meetings of the Navy Board, but was increasingly hampered by a long-term illness that caused him considerable pain.

While some records suppose that he was supported in his joining of the navy by another maternal relative, Captain George Townshend, the historian John Sugden says this was the doing of Walpole.

In 1742 Newcastle was sent to serve in the Mediterranean Sea; while at Port Mahon in March the following year Fox was given command of the 80-gun ship of the line HMS Chichester and, continuing to support Suckling's career, he took the midshipman with him on 16 June.

[3][6] While in the Mediterranean Suckling met the future Admiral of the Fleet Sir Peter Parker, at the time another junior officer, and formed a friendship that would endure throughout their respective careers.

[3][6] On 9 June the following year he moved again, joining the 80-gun ship of the line HMS Boyne at the order of her flag officer, Rear-Admiral John Byng.

He was then, on 1 November, transferred from Boyne into the 50-gun fourth-rate HMS Gloucester as the ship's first lieutenant, which the naval historian David Syrett suggests was another appointment brought about by Suckling's patrons.

[5] Suckling's position in Gloucester meant that he avoided the unemployment that came to many naval officers when the Royal Navy began to decommission warships in response to the end of the war.

[6] Gloucester sailed to join the West Indies Station on 15 May 1749, and Suckling spent the next three years of his career based in the ship at Jamaica.

In Baltimore Suckling spent most of his time patrolling the coast of the Carolinas, with occasional diversions taking him as far north as Boston.

[Note 4][8] Having left Halifax on 19 October with the rest of Boscawen's ships, Lys was separated from them in a storm but succeeded in reaching the Downs on 23 November.

[10] On 21 October 1757, Dreadnought and two other 60-gun ships of the line undertook an operation to intercept a French convoy leaving Cape Français.

[1][10][13] At this point the French commodore, Guy François Coëtnempren de Kersaint, called for one of his frigates to tow Intrépide out of the battle.

[1][10] The British lost twenty-four men killed and eighty-five wounded in the skirmish, of which ten and thirty respectively were from Suckling's command.

[10] On 1 September 1758 Dreadnought was patrolling alongside the 50-gun fourth-rate HMS Assistance when they received intelligence that the French 74-gun ship of the line Palmier was off Port-au-Prince.

[10] Suckling's fortune to find employment at the end of the War of the Austrian Succession did not now repeat itself, and he went ashore on half pay, probably living at his home in Woodton, Norfolk.

[19] As the Royal Navy began mobilising in the expectation of war against Spain, he was given command of the 64-gun ship of the line HMS Raisonnable, which was fitting out at Chatham, on 17 November.

[Note 7][24][25] This was Nelson's first sea service although Raisonnable never left the Thames Estuary during Suckling's command, which ended with the de-escalation of tensions and the decommissioning of the ship.

On 26 June Suckling was also appointed senior officer for his part of the Thames Estuary; he filled most of his time with paperwork regarding topics including naval discipline and the deployment of marine detachments.

[19][27][28] Suckling continued on in Triumph, his duties at the time of Nelson's return including hosting on board First Lord of the Admiralty John Montagu, 4th Earl of Sandwich.

[3][33] Suckling returned to half pay; he was still in his prime, a handsome and slim man despite some gout in his right hand and a thinning hairline.

[36] His hard work was done in tandem with that of Rear-Admiral Sir Hugh Palliser, his predecessor as Comptroller of the Navy and the incumbent First Naval Lord.

[1] Suckling continued to receive personal advancement during this period, being elected unopposed as member of parliament for the Admiralty-controlled constituency of Portsmouth on 18 May 1776; he never voted or made a speech during his tenure in the House of Commons.

[45] While continuing in work, from around January 1777 a long-term but undiagnosed illness had begun to take a considerable toll on Suckling's health.

Suckling is most remembered as the man who was instrumental in beginning and supporting Nelson's naval career as he grew to become a national hero.

[7] Nelson would go on to remember his uncle's conduct at Cape Français, recollecting it prior to fighting the Battle of Trafalgar exactly forty-eight years later.

With very few close relatives, his will of 1774 left bequests to his brother and some of the Walpole family, but the majority of his wealth was split between Catherine's children.