As Sir William de Borthwick, Knt, he appeared as defender on behalf of his father in an action of debt on 4 July 1476, when judgement was given against him.
They appeared again together in an action on 16 October 1479, and this time had a judgement in their favour.
[7][8] William, Lord Borthwick, as superior of the lands of Nenthorn, Berwickshire, granted a charter of them to his second son, Alexander Borthwick, upon the resignation of James Wilson, the previous feuar, on 27 June 1495.
His daughter, Agnes Brothwick, married David Kennedy, 1st Earl of Cassilis.
While his other daughter, Catherine Borthwick, married William Cunningham, 4th Earl of Glencairn.