Leonard Calvert, the second son of George Calvert first Lord Baltimore (1580?-1632), and Anne Mynne (1579-1622), was the first governor of Maryland. He was born in London in 1610. After the elder Calvert resigned his government offices and converted to Catholicism, he turned his attention to his languishing colony in Newfoundland. Leonard accompanied his father in 1628 and experienced the rigors of resurrecting the colony and a naval war with the French who had been interfering with English fishing. When his brother, Cecil, the second Lord Baltimore, decided he must remain in England to defend the Maryland charter, he entrusted the fate of his colony and the 140-160 colonists to Leonard. Baltimore's ships arrived in the Chesapeake in late February 1634. After a brief exploration, the governor took possession of the land on March 25, and Father Andrew White of the Society of Jesus celebrated Mass.

As his brother's surrogate, the young governor faced daunting problems. He had to establish the colony on a firm basis, confirm the family's land claims against hostile Virginians who opposed them, find ways to exploit the natural resources, and keep peace among a religiously diverse population, a majority of whom were Protestant. Baltimore's "Instructions," written ten days before the Ark and the Dove sailed on November 22, 1634, laid out strategies for accomplishing the Calvert vision. The governor's efforts to implement his brother's objectives all too frequently led to conflict and turmoil. He successfully negotiated the sale of land along the St. George's River, a tributary of the Potomac which the natives were about to abandon, and named the site St. Mary's. Attempts to exploit the lucrative beaver fur trade with the Indians were thwarted by Virginian William Claiborne who in 1631 established an outpost on Kent Island at the head of the Chesapeake Bay.

This led to sporadic warfare that continued until Calvert led a small force to the island in 1638 to subdue it. He enforced Baltimore's religious policy when he and the Roman Catholic councillors adjudicated an incident in favor of some Protestant servants who had been forbidden by their Catholic overseer to read aloud from a book of Puritan sermons. He attempted to maintain his brother's prerogatives as proprietor in the face of increasing opposition from Catholic and Protestant freemen in the Assembly but failed to prevent them from seizing the right to initiate legislation. His loyalty to his brother conflicted with his deference to members of the Society of Jesus who came in 1634 to bring Christianity to the natives. His inability to control the missionaries, who not only accepted land directly from the Indians but demanded privileges enjoyed by the clergy in Catholic countries, led to a sharp rebuke from his bother.

In April 1643 Calvert returned to England where parliamentary forces waged war against the king and his supporters. He conferred with his brother on ways to make the enterprise profitable and how to keep the increasingly public religious tensions in England from spilling over to Maryland. He returned in September 1644 with a commission from the king that authorized him to seize all ships and property of those in rebellion. The impecunious Calverts hoped to profit from their support of the king. English religious tensions soon engulfed the colony and prevented the governor from executing the commission. The invasion of Maryland by tobacco merchant and ship captain Richard Ingle forced Calvert to flee to Virginia. In 1646 Calvert recruited an army of Marylanders and mercenary Virginians necessary to engage Ingle. His force dispersed the remaining rebels and reestablished proprietary authority. Shortly before his death on June 9, 1647, Governor Calvert designated Catholic Thomas Greene as his successor and named Margaret Brent as his sole executrix. His best efforts, notwithstanding, Maryland remained a poor, underpopulated, and unstable society.

Leonard may have married in a Catholic ceremony during his trip to England in 1643-44. William and Anne Calvert, who claimed to be his children, emigrated to Maryland in the 1660s.

Krugler, John D. English and Catholic: The Lords Baltimore in the Seventeenth Century. Baltimore: The Johns Hopkins University Press, 2004.