Stewart served in Scottish military actions against the English in the early 15th century and was captured at the Battle of Homildon Hill, which took place on 14 September 1402 in Northumberland, England. Led by Archibald Douglas, 4th Earl of Douglas, the Scottish army had invaded England bent on plunder, in part to avenge the killing and capture of Scottish nobles in the Battle of Nesbit Moor on 22 June 1402. While returning to Scotland, they were intercepted by English forces led by Henry Percy, 1st Earl of Northumberland. The result was a decisive defeat of the Scottish army.