Merchant, Ambassador and Lord Provost of Edinburgh. Forrester was a successful merchant, making a great fortune during the reign of David II (1329-71) by trading with England, when he appears to have been greatly favoured through being allowed to import goods without the payment of duty. His first public appointment was as Justice Clerk in 1362. He originally lived in Forrester's Wynd off Edinburgh's High Street, but in 1376 he acquired the manor of Corstorphine to the west of the city, together with the lands of Whitburn and Niddry.
Forrester was appointed Lord Provost of Edinburgh (1373-78) and Sheriff of Lothian (1382). He was also served as Deputy Governor of Edinburgh Castle.
His trading with England made him the obvious candidate to act as ambassador and King Robert III appointed him Keeper of the Great Seal in 1390. He was taken prisoner at the battle of Homildon Hill on the 14th of September 1402, but intervened on behalf of his fellow prisoners and was quickly ransomed. He was knighted for his services about the same time. He was appointed Depute Chamberlain of Scotland (1405).
He died at an advanced age and was buried in the Chapel at Corstorphine which he had built and endowed in the late 14th C.