He served as Minister of Agriculture in the Rhodesian government of Ian Smith, and in 1965 was a signatory to Rhodesia's Unilateral Declaration of Independence.

[3][4][5] On 20 January 1954 he inherited his father's titles and became the 7th Duke of Montrose, taking his seat in the House of Lords on 25 June 1957.

The family lived on Derry Farm at Nyabira outside Salisbury, where the crops included maize and tobacco.

[9] During his term as Minister of Agriculture, the Land Tenure Act of 1969 was enacted, reserving the amount of land for white ownership as 45 million acres (reduced from 49 million acres) and reserved another 45 million acres for black ownership, introducing parity in theory; however, the most fertile farmland continued to be included in the white portion.

[10] Although, in an article published in Illustrated Life Rhodesia in the mid-1970s, Montrose indicated that he saw his family remaining in Rhodesia for future generations, he and his family moved to Natal, South Africa in 1979 and then to Kinross, Scotland, where he spent his final days.