He married Catherine Borthwick, daughter of Sir William Borthwick, 2nd Lord Borthwick before 10 July 1509.
William Cunningham was Lord High Treasurer of Scotland from 1526. He was sent to France to conclude a treaty for James V's marriage with Mary of Guise in 1538.
At the Battle of Solway Moss on November 24th 1542 he fought on the Scottish side and was taken prisoner. He was released for a ransom of £1000 early in 1543 and he promised to adhere to Henry VIII, who was anxious to bring Scotland under his rule. He supported the reformers and acknowledged Henry VIII as protector of Scotland in 1544. In the same year 1543 he was defeated by the Earl of Arran, and lost the Battle of Coldingham in the interests of England. He went over to the Queen-Regent.
The Clan Cunningham burned Eglinton Castle, which was home to the Clan Montgomery, to the ground in 1528 in revenge for the Clan Montgomery burning down Kerelaw castle in 1488 after Alexander Cunningham was killed along with King James III in the battle of Sauchieburn.
Sources: http://en.wikipedia.org/wiki/Clan_Cunningham http://en.wikipedia.org/wiki/Kerelaw_Castle