David Pentland was born in Libberton, Edinburgh and enlisted with the Scots Greys on 15 Apr 1807 at Edinburgh. Serving at the Battle of Waterloo in Captain Barnard's Troop, Pentland was discharged on 15 Apr 1817.
The charge of the Scots Greys played a pivotal role in Wellington's victory at Waterloo. Attacking Marcognet's Division of D'Erlon's Corps with such ferocity that, assited by the Royals and Inniskilling Dragoons, the Union Brigade routed the French 45th Regiment andf captured their eagle. However, the Scots Greys continued through ranks of French cavalry and lancers, and some onto the artillery positions. Isolated and exhausted, men and horses were cut down. Ponsonby himself was killed, passing his snuff box and wife's miniature portrait to Major of Brigade Thomas Reignolds, who was subsequently killed himself. 105 men of the Scots Greys lost their lives, with a further 93 recorded officially as wounded.