[2] David Leslie re-appeared in the Swedish army in 1634 where he served as a colonel and thereafter Field Marshal Johan Banér's adjutant-general with whom he participated in the Battle of Wittstock in 1636.

The Swedish Riksråd (Royal Council) records show that he and Colonel James Lumsden asked to return to Scotland at the same time.

[3] The Stuart ambassador in Hamburg, Sir Thomas Roe, informed London of Leslie's departure with Colonel Lumsden and 24 other Scottish officers from that city.

He played an important role at the critical Battle of Marston Moor, west of York by leading a successful cavalry charge against the Royalist Cavaliers while Oliver Cromwell was wounded.

[4] This allowed the infantry time to regroup and eliminate the Royalist battalia led by another former colleague, Lieutenant General James King, Lord Eythin.

He routed the main Royalist force under James Graham, Marquis of Montrose at the Battle of Philiphaugh (September 1645) and was rewarded by the committee of estates with a present of 50,000 merks and a gold chain; but his victory was marred by the butchery of the captured Irish—men, women and children—to whom quarter had been given.

[1] When Earl of Leven left for Newcastle upon Tyne Leslie took over command of the Scottish army besieging Newark.

When MacNab found that it would not be possible to maintain defence, he led the defenders, sword in hand at the head of 300 men, who cut their way through the besieging force.

Whilst Montrose was being led to his death Leslie dispatched five troops of horse, including some from Holborne's and the John Gordon, 14th Earl of Sutherland's regiments to Dunbeath Castle.

When the Parliamentarian army under Oliver Cromwell invaded Scotland in July 1650 Leslie commanded the Scottish forces.

Although the Scottish army had twice as many men, divisions within the Committee of Estates and Kirk instructing Leslie gave Cromwell the opportunity to inflict a decisive defeat on the Scots at the Battle of Dunbar on 3 September 1650.

Leslie escaped with a tiny remnant of his army which then joined Charles II's Royalist forces in the Stirling area.