He was a Commissioner for the Treaty of Peace with Anna of Oldenburg, signed at Aberdeen 19 October 1556 confirmed by Mary, Queen of Scots, 26 September 1557.
With James MacGill, he prepared a short guide to Scottish law, the Discours Particulier D'Escosse, written in French for Mary, Queen of Scots, and Francis II of France.
[2] After the Siege of Leith, in the articles of the Treaty of Edinburgh, Bellenden was nominated to negotiate the French withdrawal from Scotland on behalf of the Lords of the Congregation.
In February 1572, during the Marian Civil War, Regent Mar sent him and Robert Colville of Cleish to greet two English ambassadors, Thomas Randolph and William Drury, in Edinburgh and invite them to supper.
And to the eldest son of the third marriage he left the barony of Carlowrie, (Linlithgowshire), and Kilconquhar, Fife, and diverse lands about Brechin."