According to historian Elizabeth Griffiths, Lawrence was seen as a "competent", "efficient" officer with a "service record that had earned him fairly rapid promotion, a person of considerable administrative talent who was trusted by both Cornwallis and Hopson.

He participated in the Battle at Chignecto (1749) and then built Fort Lawrence on the south bank of the Missaguash River in the fall of 1750, and was promoted lieutenant-colonel the same year.

During the French and Indian War, in conjunction with Governor William Shirley of Massachusetts, he helped raise forces for the Battle of Fort Beauséjour on 16 June 1755.

In 1757, Lawrence was further promoted to the title of brigadier general and commanded one of the three divisions at the successful siege of the French fortress at Louisbourg on Île Royale (Cape Breton Island) in 1758.

According to his biographer, Dominique Graham, Referring to the monument raised to Lawrence’s memory in St Paul’s Church, Halifax, to indicate the late governor’s popularity, Belcher wrote, "In a grateful sense of his affection and services the last tribute that could be paid to his memory was unanimously voted by the General Assembly at their first meeting after the late Governor’s universally lamented decease."