Walter returned to Scotland in 1366, and was warmly welcomed back by King David. The king was fascinated by the cult of the crusader, and Walter's previous exploits had already made him one of the royal favorites. As a reward for his latest adventures, King David married him to Euphemia, daughter and heiress to Uilleam III, Earl of Ross, who was bullied by David into allowing the marriage. The marriage took place on September 13 of the same year. When King David died in 1371, Walter may have been worried that the new king, Robert Stewart, who was an ally of Earl Uilleam's, may have rescinded the patronage. However, the new king did not, and when Earl Uilleam died in 1372, his wife inherited the title, and he became Lord of Ross.
Walter died at Perth on February 27, 1382. He left two children, Alexander (the future Earl of Ross) and Mariota, who would marry Domhnall, Lord of the Isles. Although Alexander did eventually inherit the Earldom, after Walter's death, de facto control of the Ross passed temporarily into the hands of Alexander Stewart, Lord of Badenoch, who married Countess Euphemia.