Barret was likely introduced to the Marquess of Rockingham by Edmund Burke, who had become his private secretary. The Marquess' s Irish seat was at Coolatin, Co. Wicklow. Barret was employed to draw the remains of Killtimon Castle, Co. Wicklow, and a copy after his drawing survives in the Royal Irish Academy An oil painting by Barret, with a wooded mountainous river landscape with anglers by a waterfall in the foreground and a ruined tower house in the distance, which relates to these views, was sold in 2003.