Stockton's grandfather,
Harold Macmillan, 1st Earl of Stockton, who had served as
Prime Minister of the United Kingdom from 1957 to 1963, unexpectedly accepted a peerage in February 1984, at the age of ninety. His son
Maurice Macmillan died three weeks later, making Stockton the heir to the new earldom, and he succeeded as a member of the
House of Lords on his grandfather's death at the end of 1986. However, he is not recorded as having spoken in any debates there, and was one of the hereditary peers who lost their seats as a result of the
House of Lords Act 1999. Having been beaten at
Bristol in
1994, he went on to be elected as a
Conservative member of the
European Parliament for
South West England from
1999 to
2004. Stockton has been an unsuccessful candidate sixteen times in the
by-elections held among hereditary peers for a seat in the House of Lords, as of 2019. Most notably, in 2007 he came third in a contest to replace
Lord Mowbray, behind the winner,
Lord Cathcart, and
Lord Younger of Leckie; in the 2010 by-election to replace
Lord Northesk, he came second behind
Lord Younger of Leckie; in 2011 he lost to
Lord Hanworth in a ballot for the seat of the deceased
Lord Strabolgi; and in 2014 he lost out to the
Earl of Oxford and Asquith. At the
May 2011 local council elections, Stockton was elected as a Conservative councillor of
South Bucks district council and represented the Denham South ward for four years, but did not stand at the
2015 local elections. Both his father
Maurice Macmillan (1921–1984) and his grandfather preceded him as chairmen of
Macmillan Publishers Ltd., the publishing house long owned by the family. Stockton sold it to the German
Holtzbrinck group. He ranked 253rd in the
Sunday Times 2004 Rich List, with an estimated wealth of £165m. Stockton renovated
Hayne Manor with his second wife in
Devon and listed it for sale. On 29 April 2002, Stockton appeared alongside several other relatives of deceased former prime ministers, as well as then-prime minister
Tony Blair and the four surviving former prime ministers at the time (
Edward Heath,
James Callaghan,
Margaret Thatcher and
John Major), for a dinner at
Buckingham Palace which formed part of the celebrations for the
Golden Jubilee of Elizabeth II. Stockton is vice president of the
Royal Crescent Society, Bath. ==Personal life==