The early career of Thomas Teddeman is unknown; he was not a naval captain during the First Anglo-Dutch War.

In 1665, during the Second Anglo-Dutch War, he distinguished himself as rear admiral of the Blue Squadron in the Battle of Lowestoft, with as flagship the new second rate HMS Royal Katherine, and was knighted on 30 June (Old Style).

In August 1665 Teddeman was sent on the Revenge to Bergen to capture a Dutch treasure fleet with a flotilla of frigates but was defeated in the Battle of Vågen by Commandeur Pieter de Bitter.

Though this was a major disappointment to Charles II of England, Teddeman's career did not suffer much and he fought, again on the Katherine, the next year as vice admiral of the Blue in the Four Days Battle and as vice-admiral of the White in the St James's Day Battle.

In 1668 he commanded on HMS Cambridge, but was the subject of an investigation by English Parliament, trying to establish the causes of the lost war, by which he was much troubled.