William Douglas Cullen was educated at the High School of Dundee and the universities of St Andrews and Edinburgh.

He was admitted to the Faculty of Advocates in 1962 and was Standing Junior Counsel to Her Majesty's Customs and Excise from 1970 to 1973.

[5] In March 2002, Lord Cullen led the 5-judge tribunal at the Scottish Court in the Netherlands which heard the failed appeal of Abdelbaset al-Megrahi against his conviction for the 1988 Lockerbie bombing of Pan Am Flight 103.

On 25 June 2005, he was elected president of the Saltire Society, replacing The Right Honourable The Lord Sutherland of Houndwood, K.T.

[12] On 4 September 2009 he was also formally installed as chancellor of Abertay University in Dundee, a position he held for a decade.