Lord Powerscourt sat in the House of Lords as one of the Irish Representative Peers until 1884, when he was created a peer of the United Kingdom. He was a Justice of the Peace in both co. Wicklow and Dublin, and acted as one of the Lord Justices of Ireland.
He completed the magnificent gardens at Powerscourt, remodeled the interior of the house to a great extent, adding a wing and creating a new dining room. Following in his father's footsteps, he employed the drunken and eccentric architect Daniel Robertson to direct the works. In spite of his success, the 7th Viscount noted that Robertson was 'always in debt and…used to hide in the domes of the roof of the house' to escape the Sheriff's officers who pursued him. By then he was crippled with gout and in an advanced state of alcoholism; at Powerscourt he 'used to be wheeled out on the terrace in a wheelbarrow with a bottle of sherry, and as long as that lasted he was able to design and direct the workmen, but when the sherry was finished he collapsed and was incapable of working till the drunken fit had evaporated.' (MS notes by Mervyn, 7th Viscount Powerscourt, in IAA, Powerscourt Album 1 (Acc. 89/62).