Lockhart was transformed by inheritance from his cousin into a wealthy landowner whose estates were estimated as producing £14,000 p.a.
I again state, that I shall support the present administration, that I have supported them in Lanarkshire, that I neither vote in Edinburgh or Argyll, as there is no opposition, and that I therefore expect to be supported by government.
Grenville, already engaged to Alexander Allan, was unable to help him and Lockhart himself asked Viscount Howick for local support, assuring him: ‘I exert every nerve in support of the present ministry’.
Apart from his professed support of the Grenville ministry in 1806, Lockhart subsequently voted only with government. In January 1808 he informed Lord Melville of his intention to remain for a time in Scotland after the opening of the session, and in October 1809 requested a surveyorship of taxes for his brother Norman.
He died 22 June 1816, aged 40, from injuries received in a carriage accident.
