As he was illegitimate, he was not able to inherit his father's title or estates, which passed instead to his half brother Frederick Calvert, 6th Baron Baltimore (1731–1771).

Benedict Calvert spent most of his life as a politician, judge and planter in Maryland, though Frederick, by contrast, never visited the colony.

Calvert became wealthy through proprietarial patronage and became an important colonial official, but he would lose his offices and his political power, though not his land and wealth, during the American Revolution.

His birth year has been variously given as 1724, 1730 and 1732, but the grave stone in the floor of the chancery of St. Thomas Episcopal Church in Croom, Maryland gives the date of January 27, 1722.

H. S. Lee Washington, writing in the New England Historic Genealogical Society Register in July 1950, speculates that she was Melusina von der Schulenburg, Countess of Walsingham,[2][3][4][5] the daughter of George I of Great Britain and his mistress, Melusine von der Schulenburg, Duchess of Kendal.

[7] In around 1736 or 1737,[8] the young Benedict was sent to the Calverts' proprietary colony of Maryland, which in the mid 18th century was still a somewhat sparsely settled, largely rural society.

According to the letters of Rosalie Stier Calvert, Benedict was personally escorted to Annapolis on a frigate commanded by Admiral Edward Vernon, though this seems unlikely.

[10][11][12] On arrival, the boy was placed in the care of Dr George Steuart (1700–1784), an Edinburgh-trained physician and a political ally of the ruling Calvert family.

[17]On April 21, 1748, Benedict and his cousin Elizabeth Calvert were married in St Ann's Church by the Reverend John Gordon.

[27] According to the writer Abbe Robin, who travelled through Maryland during the Revolutionary War, men of Calvert's class and status enjoyed considerable wealth and prosperity: [Maryland houses] are large and spacious habitations, widely separated, composed of a number of buildings and surrounded by plantations extending farther than the eye can reach, cultivated...by unhappy black men whom European avarice brings hither...Their furniture is of the most costly wood, and rarest marbles, enriched by skilful and artistic work.

Washington himself did not approve of the match owing to the couple's youth, but eventually gave his consent,[30][32] and was present at the wedding celebrations, which took place at Mount Airy.

In 1774, as collector of customs for the Patuxent River, Calvert wrote to the British authorities, describing the burning of The Peggy Stewart on October 19, 1774, the event which became known as the "Annapolis Tea Party".

[37] After the war's end, Calvert had to pay triple taxes as did other Loyalists, but he was never forced to sign the loyalty oath and his lands and property remained unconfiscated.

In 1783, after the war was over, Washington stayed with the Calverts at their Mount Airy plantation, shortly after resigning his commission in Annapolis on December 23.