On January 6, 1759, Washington married the wealthy widow Martha Dandridge Custis, then 28 years old. Surviving letters suggest that he may have been in love at the time with Sally Fairfax, the wife of a friend. Nevertheless, George and Martha made a compatible marriage, because Martha was intelligent, gracious, and experienced in managing a planter's estate.

Together the two raised her two children from her previous marriage, John Parke Custis and Martha Parke Custis; later the Washingtons raised two of Mrs. Washington's grandchildren, Eleanor Parke Custis and George Washington Parke Custis. George and Martha never had any children together – his earlier bout with smallpox in 1751 may have made him sterile. The newlywed couple moved to Mount Vernon, near Alexandria, where he took up the life of a planter and political figure.

Washington's marriage to Martha greatly increased his property holdings and social standing, and made him one of Virginia's wealthiest men. He acquired one-third of the 18,000-acre (73 km2) Custis estate upon his marriage, worth approximately $100,000, and managed the remainder on behalf of Martha's children, for whom he sincerely cared.

Throughout the world, men and women were saddened by Washington's death. Napoleon ordered 10 days of mourning throughout France; in the United States, thousands wore mourning clothes for months. To protect their privacy, Martha Washington burned the correspondence between her husband and her following his death. Only a total of five letters between the couple are known to have survived, two letters from Martha to George and three from him to Martha.

On December 18, 1799, a funeral was held at Mount Vernon, where his body was interred. Congress passed a joint resolution to construct a marble monument in the United States Capitol for his body, supported by Martha. In December 1800, the United States House passed an appropriations bill for $200,000 to build the mausoleum, which was to be a pyramid that had a base 100 feet (30 m) square. Southern opposition to the plan defeated the measure because they felt it was best to have his body remain at Mount Vernon.