He succeeded his father some time before 22 November 1429, and in August 1430 he was, jointly with his brother-in-law, Sir Robert Cunningham of Kilmaurs, appointed governor of Kintyre and Knapdale.
With the other Scottish commissioners he received the present of a silver cup from Henry VI of England.
On 5 February 1444 he had a safe-conduct to go to Durham to treat for the extension of the truce and the return of the Scottish hostages.
[2] In 1444 Montgomerie was appointed keeper of Brodick Castle on the Isle of Arran.
He was one of those who set their seals to instruments passed by the parliament held at Perth, Scotland on 9 June 1445 against the lords who had rebelled against James II.