Sir Walter was one of the hostages for King James I on 28 March 1424 and was exchanged and permitted to return to Scotland on 16 July 1425.

He is named as one of the Scottish Commissioners to meet the English at Hawdenstank with 800 men to redress complaints, in a Safe-Conduct dated 24 January 1430 (1429/30).

He remained Lord High Treasurer until 1449, a post which he could not hold unless he was also a Privy Councillor.

He married Lady Isobel, daughter of the Regent, Robert Stewart, Duke of Albany and wife Margaret Graham, Countess of Menteith, who was also the widow of Alexander Leslie, Earl of Ross (d. 1402).

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