He was elected to his father's seat for Anne Arundel County in the Maryland Assembly, legislature in Annapolis for the colony.

In 1760 he completed construction of his summer home and estate at "Georgia Plantation", southwest of Baltimore along the Georgetown Road, also known as the Columbia Road (later Washington Boulevard, (U.S. Route 1) in modern Carroll Park and north of the Gwynns Falls stream which flows into the Middle Branch ("Ridgeley's Cove") and Ferry Branch of the Patapsco River.

Carroll continued in the Assembly until it was prorogued at the beginning of the Revolution, and then met with other leaders in the Annapolis Convention and had important roles in all their sessions.

Then, in an action typical of his style, he entertained the governor and his wife as house guests at Mount Clare Mansion until they sailed for England.

His funeral was held at Old St. Paul's Anglican Church (now Episcopal since 1789) in Baltimore at North Charles and East Saratoga Streets.

In the early 1760s, Carroll took the lead and encouraged a group of his business associates to build a fund for a young saddler, Charles Willson Peale, so that he could go to Europe and study painting.

Their home today is a museum, (both for its architecture, furniture and decorations plus history of the plantation and family) operated since 1917 by the National Society of the Colonial Dames in the State of Maryland, on behalf of the owner which is the City of Baltimore and its Department of Recreation and Parks.

The home is a fine example of Georgian architecture, and stands on a rise in the center of Carroll Park in southwest Baltimore City, surrounded by the neighborhoods of "Pigtown", (so named for being the site of butcher shops and meat packing plants to process pigs transported from the Midwest on the B&O Railroad);[2] the neighborhood was also known by its more recent "gentrified" name of Washington Village.