Captain Sir Thomas Liddell, 1st Baronet (1578 - 1652) was an English politician, a member of the Liddell family which monopolized the local government of the North of England during the 16th and 17th centuries. He was one of the leading supporters of the Royalist cause in the English Civil War.
Liddell was born in 1578, the son of Thomas Liddell (d.1619) and his wife Margaret Watson, daughter of John Watson, Alderman of Newcastle. His paternal grandfather, Thomas Liddell of Newcastle-upon-Tyne (d.1577) was a merchant adventurer who had served as Sheriff of Newcastle in 1563-64 and Mayor of Newcastle in 1572-3. His father, Thomas (d.1619), also a merchant, made vast profits from corn and coal and bought the Ravensworth Castle in 1607 and also served as Sheriff of Newcastle in 1592-93 and Mayor of Newcastle in 1597 and 1609.
A Catholic Recusant, he succeeded to Ravensworth Castle in 1615 on the death of his father. He also owned the Redheugh estate in County Durham. He was admitted to Gray's Inn on 15 March 1620.
Liddell served as Sheriff of Newcastle-upon-Tyne in 1609 and Mayor of Newcastle-upon-Tyne in 1625, 1634, and 1636. In April 1640, was elected Member of Parliament for Newcastle-upon-Tyne in the Short Parliament. He was created a baronet on 2 November 1642.