When the British took control of West Florida after the war, Browne sponsored French Huguenot and Irish immigrants to the area.
Browne in 1768 led a successful expedition to the region of Natchez, bringing back a report of the fertility of the land and its lack of population, and suggesting that it be developed.
For his services in the war he had been awarded 20,000 acres (8,100 ha) in the province, and he used the trip to stake out large parcels of land on the eastern banks of the Mississippi River, just north of present-day Baton Rouge, Louisiana.
He spent much of the next two years in England, having his finances scrutinized by the colonial office, and continuing to drum up interest in settlements on the Mississippi.
There was public speculation on both sides of the Atlantic that the Mississippi lands would eventually be separated into their own province, with Browne as its governor.
With 12 other high-ranking hostages from the island he was taken back to the Chesapeake Bay by the American fleet, and was released, in part, by the efforts of his friend Timothy Hierlihy, in exchange for William Alexander.
Browne formed the Loyalist Prince of Wales' American Regiment, served at the siege of Rhode Island, and spent some time in Florida before finally returning to the Bahamas to resume his post there in July 1778.
He then faced accusations of cowardice and incompetence for his conduct of the battle and, after dismissing his council in an attempt to scotch the rumours (an unprecedented move), he was replaced by John Robert Maxwell two years later in 1780.