Wightman began his military career in 1690 when he was commissioned as Ensign in the First Foot Guards to Lt-Colonel Fraser Wheeler.

This mattered in a world where rank and structure were extremely important in both civilian and military life; it also suggests Wightman came from an influential family.

[1] This was an Allied defeat with heavy casualties for those involved and on 7 August Wightman was promoted to Lieutenant with additional rank of Capt.

On 30 August it participated in a very bloody assault on Terra Nova in which Colonel Courthorpe was killed and Lieutenant-Colonel Matthew Bridges was severely wounded.

Its Colonel Blood continued to serve as brigadier-general and When the 1715 Jacobite rebellion broke out he commanded the first reinforcements sent to assist the Duke of Argyll at Stirling.

During the 1719 Rising he commanded the pro-Hanoverian forces that defeated the Jacobites at the Battle of Glen Shiel in June that year.