Seymour maintained a reputation as a courageous and innovative officer: he was awarded a commemorative medal for his actions at the battle of the Glorious First of June and is credited with introducing epaulettes to Royal Navy uniforms as a method of indicating rank to non-English speaking allies.

In his youth he formed close personal friendships with fellow officer John Willett Payne and George, Prince of Wales, through association with whom he gained a reputation as a rake.

He was initially educated at Bracken's Academy in Greenwich, where he met lifelong friend John Willett Payne, before joining the Navy at age 11 at his own insistence.

The only major operation in which he participated during the period was the conclusion of the Great Siege of Gibraltar, when Latona was attached to Lord Howe's fleet that relieved the fortress.

[2] During this service, Seymour was repeatedly engaged in scouting the Franco-Spanish fleet in Algeciras, a task made difficult by bad weather and the erratic movements of the enemy.

[4] In the Spanish armament of 1790, Seymour was called to service in command of the ship of the line HMS Canada, opening his commission with a cruise off the Isle of Wight.

The head injury rendered him unable to endure any loud noises or bright lights and for the next three years he lived as an invalid at his country estate in Hambledon.

[2] Transferred to the Channel Fleet, Leviathan was attached to service under Lord Howe and served with him during the Atlantic campaign of May 1794 alongside John Willett Payne, captain of HMS Russell.

The campaign culminated in the Glorious First of June, when a French fleet was defeated by Howe's innovative tactics, but was ultimately successful in protecting a large grain convoy from the United States.

[13] In 1796, Seymour was employed in the search for the French fleet which attempted and failed to invade Ireland, but Sans Pareil was badly damaged in a collision with HMS Prince during the campaign and had to be decommissioned for extensive repairs.

[2] Seymour's body was taken from Jamaica on the morning of 17 September 1801, for return to Britain aboard HMS Pickle (originally a Bermudian-built merchant vessel named Sting)[20] and joined that of his wife, who had died in Bristol a few days before her husband's death.

[2] His extensive estates were dispersed amongst his seven children, of whom six survived him: Seymour's death was widely mourned among his contemporaries, Lord St. Vincent once describing him as "an excellent officer".