David Leslie, 1st Lord Newark (c. 1600–1682) was a cavalry officer. He fought for the Swedish army of Gustavus Adolphus during the Thirty Years' War. He had entered Swedish service in 1630, serving as a captain in the regiment of Alexander Leslie (future Earl of Leven). He returned to Scotland just before the end of the Bishops' War, and participated the English Civil War and Scottish Civil Wars.
David Leslie was one of the Scots who transferred from Swedish to Russian service under Alexander Leslie of Auchintoul (not to be confused with Leven) in 1632 to participate in the Smolensk War and was mentioned by name in Leslie of Auchintoul's testimonial. 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 at Wittstock in 1636.
Leslie petitioned to leave Swedish service in August 1640 after being wounded in battle. The Swedish Riksråd (Royal Council) records show that he and Colonel James Lumsden asked to return to Scotland at the same time. The seriousness of Leslie’s wounds are questionable and it is likely that they were summoned home to support Alexander Leslie's Army of the Covenant, then participating in the Bishops' Wars against Charles I. Both these officers were rewarded with a severance deal which included 200 muskets and 200 suits of armour each. Leslie also received a valuable gold chain as an indication of his loyal service to the Swedish Crown. 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. They arrived in Scotland after the Bishops' Wars had effectively ended.
After the parliaments of Scotland and England agreed the Solemn League and Covenant in 1643, David Leslie became a Major General under Alexander Leslie (now Earl of Leven) in the Army of the Solemn League and Covenant which was sent to fight alongside the forces of the English Parliament in 1644. 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. This allowed the infantry time to regroup and eliminate the Royalist battalia led by another former colleague, Lieutenant General James King, Lord Eythin. David Leslie subsequently commanded the force that besieged Carlisle, Cumbria.