Robert Throckmorton may have trained at the Middle Temple, the inn attended by his father. At least three of his younger brothers and his own eldest son trained there, but as the heir to extensive estates, he had little need for a career in justice or government. He was joined with his father in several stewardships from 1527 and was perhaps the servant of Robert Tyrwhitt, a distant relative by marriage of the Throckmortons, who in 1540 took an inventory of Cromwell's goods at Mortlake. He attended the reception of Anne of Cleves. With several of his brothers he took part in the French war of 1544. Three years later he was placed on the Warwickshire bench, and in 1553 appointed High Sheriff of Warwickshire. He was also elected as a knight of the shire (MP) for Warwickshire in 1553 and 1555. Three of his brothers likewise sat for Parliament, Nicholas as knight of the shire for Northamptonshire.