Lawrence married Anne Fairfax, whose father, Colonel William Fairfax, exerted a great influence on George Washington. The Fairfax family helped launch George Washington's career as a government surveyor.
In 1751, George traveled to Barbados with Lawrence, who suffered from tuberculosis. George caught a minor case of smallpox, which sickened and scarred him, but saved him from worse disease later in life. A year later, Lawrence returned from the tropics to Virginia, where he died, leaving George in control of the family plantation.
Washington inherited his brother's position as Adjutant and became a major in the army. In 1754, militiamen under his command ambushed a French patrol who were encroaching a nearby fort, and it became the first battle of the French and Indian War. Later that same year, Washington surrendered to the French at the Battle of Fort Necessity, but mistakenly signed a document saying their commander was "assassinated."
(Fun fact: Washington's allies fired first and without provocation. This guy was cursed from the get go. -V.)