In the following year Dubhghall mac Suibhne granted to the earl the lands of Skipnish, Killislate, and others, being that part of Kintyre called South Knapdale and the parish of Kilcalmonell. Following on this, the Earl granted the church of Kilcalmonell at Clachan to the monks of Paisley. He also made grants to Kilwinning Abbey of churches in Knapdale, which show that he had possession of North Knapdale also. About 1263 the earl was Sheriff of Ayr, and aided in making preparations to repel the expected invasion of King Haakon IV of Norway. He and his brother Alexander Stewart, 4th High Steward of Scotland were joint commanders of the Scots in the Battle of Largs. The earl was Sheriff of Dumbarton in 1271 until 1288. On 25 July 1281 he was one of the witnesses to and guarantors of the marriage contract of the Princess Margaret with Eirik II of Norway. He, Countess Mary, and a party of Scots barons traveled to Norway accompanying the princess and her dowry of fourteen thousand marks. In 1285 he and his Countess were again attacked by the rival claimants William Comyn and his wife Isabella, their claim having been in 1282 pressed upon King Alexander III of Scotland by the English King, and in a Parliament at Scone it was decided that the earldom should be divided into two portions.