St Lo entered on a naval career, and after service in the Mediterranean on several ships, rose to the rank of captain with his own commands.

After time in France as a prisoner of war, he returned to England and took up various political positions, while writing about his observations and thoughts on naval administration.

As commissioner at Plymouth he had an important role in supporting the construction of the first Eddystone Lighthouse, but when he sent the project's guardship away, the crew and the architect, Henry Winstanley, were promptly captured by a French privateer.

St Lo's parentage brought him the important patronage of Laurence Hyde, 1st Earl of Rochester, which aided his rise through the navy.

St Lo entered the navy and after a period of service, was appointed as lieutenant of HMS Phoenix on 16 January 1678, serving in the Mediterranean in operations against the Barbary States.

[3] The commander in the Mediterranean, Admiral Arthur Herbert, moved St Lo into the 46-gun HMS Hampshire under Captain Sir George Rooke, but while serving on her in May 1681, he found himself accused, with another officer, of having committed a murder in Tangier.

Russell had been profiting from the widespread piracy going on in the Caribbean waters, causing St Lo to criticize this as an abuse of his authority.

[2][3] The Portsmouth was attached to the fleet under Admiral George Legge, 1st Baron Dartmouth, based in the River Medway during the events of the Glorious Revolution.

Legge failed to intercept the fleet bringing William of Orange to Britain, with St Lo later declaring himself an avowed supporter of the new regime.

He was present at the Battle of Bantry Bay on 1 May 1689, but while in the English Channel in August 1689, Portsmouth was attacked by the 58-gun French ship Marquis, and was captured.

"[3]St Lo was back in England by September 1692, as in this month he presented to the Privy Council proposals for raising 20,000 seamen for the navy without having to resort to impressment.

[1][2][6] His posting here was delayed for two months though as an investigation was taking place into alleged abuses during his time as a prize commissioner, for which he was eventually acquitted.

[1] An appointment as resident-commissioner at Plymouth followed in 1695, and in 1697 he received orders to assist in the building of the first Eddystone Lighthouse, to the design drawn up by Henry Winstanley.

[2][6] St Lo was required to provide protection for the workers on the exposed rock, and he assigned the 26-gun HMS Terrible to this task.

[2][7] Word of Winstanley's capture is supposed to have reached King Louis XIV, who ordered his release with the comment "France is at war with England, not with humanity.

[9] St Lo suggested that "two or three Small vessels [with] good sailors [should be sent] to cruise up & down, [and] examine all Sloops & Boates passing to & fro.

[1] St Lo had been appointed an equerry to Prince George of Denmark by 1700, a post he held until c. 1704, and in 1703 moved from Plymouth to Chatham, still serving as a resident commissioner.

[2] Another reprimand came after his move from Plymouth to Chatham, for taking with him both the new dockyard yacht, HMS St Lo, and items of official correspondence.

[2] His assertive nature was further illustrated in an incident when he confronted striking dockyard workers at Chatham with a drawn sword, and chased them from the yard.