Between 1794 and 1806 he served as aide-de-camp to Lieutenant General Sir James Craig, whose duties as military commander and colonial administrator took him to the Cape of Good Hope, Bengal, the East Indies, Gibraltar, Malta, Naples and Sicily.
He wrote to Prévost on 20 May 1812, "...I have purchased all the green cloth in this place (Quebec) and have commissioned a sufficient quantity to equip the regiment to render it efficient for immediate service.
In July 1812, Prévost was notified that the British Government had revoked some of the orders in council which the Americans had cited as one of the causes of the war.
Baynes went to Albany, New York, under a flag of truce to negotiate an armistice with Major General Henry Dearborn, commanding the United States' armies in the north.
During a visit to Kingston in Upper Canada in May 1813, Prévost and Commodore Sir James Lucas Yeo, commanding the British naval units on Lake Ontario, became aware that there was an opportunity to capture and destroy Sackets Harbor, New York.
At Champlain, New York, Brigadier General William Henry Winder claimed to have no authority to agree to any pact, and the British government subsequently disavowed the negotiations.
This was resented by many of the recently arrived British commanders, who had seen far more fighting in the Peninsular War than Baynes had experienced during his career.
Most of the British commanders considered that Prévost and his staff (including Baynes) had planned and executed the operation badly.