He succeeded to the title upon his father's death in 1963, sitting in the House of Lords first as a cross-bencher, then as a Liberal, and finally, from 1972, as a Conservative.

He championed causes from the abolition of capital punishment to restrictions on onshore wind farms.

He also served as a delegate to the Council of Europe, living at the family's Dutch estates in Ophemert.

In 1991, he was moved by her successor, John Major, to the Department of Trade and Industry as a Parliamentary Under Secretary of State, but he left the government at the 1992 general election.

His heir is his son, the Honourable Alexander Shimi Markus Mackay (born 21 April 2010).