Bladen was born in Maryland in 1698, the eldest son of William Bladen of Annapolis, who came to Maryland in 1690, and his wife Anne Van Swearingen. Among his siblings was Anne Bladen. Thomas was the grandson of Nathaniel Bladen and Isabella Fairfax. He was the nephew of Colonel Martin Bladen, Commissioner of the Board of Trade and Plantations. Bladen travelled early to England in 1712, where he was educated at Westminster School. He disposed of his Maryland property on his father's death in 1718.
In 1742, Bladen returned to Maryland as provincial Governor, on the recommendation of his brother-in-law, Lord Baltimore. He was the first governor to be born in the Province. He also served as surveyor general, Western Shore, 1742–1746, and chancellor, 1742–1746/47. While governor, he concluded a peace with the Six Nations. He negotiated with Pennsylvania authorities for the settlement of the Maryland–Pennsylvania boundary. Upon his arrival in Maryland, the Legislature awarded him £4,000 to build himself a residence, which was £1,000 more than his predecessor. In 1744, he bought of land in Annapolis from Stephen Bordley and commenced construction of a building, now McDowell Hall, St. John's College, as a governor's residence. He quickly disagreed with the Legislature about its architecture and became involved in a lawsuit with Bordley, the previous owner, and construction halted. While as governor in Maryland in 1744, Bladen organized the first ice cream social in the United States. The social was organized while at a dinner party. Bladen quickly became an unpopular Governor and was dismissed from office by October 1746 because he was "tactless and quarrelsome". He returned to England in 1746, when he was succeeded by Samuel Ogle - husband of his niece Anne Tasker. Ogle had been Governor prior to Bladen's arrival in Maryland.
Bladen lived at Leyton Grange in England where he died in 1780 and was buried in the churchyard of St Mary's Leyton. Bladen's wife Barbara, who had a life interest in Glastonbury, died in 1783 and their heirs were their daughters Barbara and Harriet who sold the whole estate in 1799.
Legacy
The Governor's residence sat uncompleted until 1766 when the roof collapsed. The building now serves as the central hall of St. John's College and is named McDowell Hall. The nickname for McDowell Hall is "Bladen's Folly". The town of Bladensburg, Maryland, which was incorporated in the first year of his governorship as Garrison's Landing, was renamed after him.