Sackville was also disappointed when Lord Wilmington the late Prime Minister (d. 1743) declined to leave him his Sussex estates, worth £3-£4,000 a year. It is not clear if Wilmington's decision was made because of Sackville's messy private life, or his political inconstancy. Commissioned a captain in the 37th Regiment of Foot in 1734, he became a captain and lieutenant-colonel in the 2nd Regiment of Foot Guards on 1 May 1740. He disgraced himself by deserting from the Guards when they were sent on foreign service in 1746, and was forced to leave the Army in September. Finally, he was committed to a private lunatic asylum circa 1746, then sent abroad to exile on a very small allowance in Lausanne where Lord Shelburne met him in 1760, and commented on his dirty condition but lucid conversation.