After recovering, he continued to serve as lieutenant aboard several ships and smaller craft on the North American station.

After war with America broke out, the Commander in Chief on the North American station (Admiral Sir John Borlase Warren, 1st Baronet), detached Barclay and two other lieutenants (Robert Finnis and Daniel Pring) to act as "Captains of Corvettes" on the Great Lakes.

Although the Americans had no armed vessels on the lake, they were constructing two large brig-rigged corvettes at Presqu'Isle, and also transferring several from Black Rock on the Niagara River.

He first reconnoitred Presqu'Isle, and determined that it was defended by an entrenched force of 2000 militia, and the two American brigs had their lower masts fitted.

He then proceeded to intercept the American ships from Black Rock, but missed them in hazy weather, although at one point the two forces were apparently only fourteen miles apart off the Cattaraugus Creek.

[3] For the next few weeks, Barclay maintained a blockade of Presqu'Isle, preventing the Americans under Oliver Hazard Perry from crossing the sandbar at the mouth of the harbour.

Finally in September, Barclay had received a last reinforcement of a few officers and sailors and part completed a ship-rigged corvette, but no food remained at Amherstburg.

In August 1815, he married his first cousin, Agnes Cosser, at St John the Evangelist, Smith Square, City and Liberty of Westminster[4] and they had several children.