Keigwin was a man of good Cornish family, who had entered the King's navy in 1665, and taken part in Monk's memorable four days' battle against the Dutch in the following year.

When St.Helena was recaptured from the Dutch (1673), he had distinguished himself in command of the boats that made the attack, and was left as Governor of the island till it was taken over by the East India Company.

As a reward for his services, the Company made him their military commandant at Bombay.

Two years later again, the Company, in a fit of economy, reduced their military establishment to two lieutenants, two ensigns, and one hundred and eighty-eight rank and file.
The troop of horse was disbanded, Keigwin was discharged from the service, and thirty soldiers, who had been detached to Surat to defend the factory against Sivajee, were refused any extra allowance, which caused much discontent.

Before long the Directors became alarmed at the defenceless state of Bombay, and sent out Keigwin again with troops and artillery, to have the chief military command and the third seat in Council.