Son of a Scottish nobleman, the handsome Carr first attracted James's interest in 1607. The King soon made him a gentleman of the bedchamber, and thereafter he rose rapidly in royal favour, becoming Viscount Rochester in 1611 and a privy councillor in April 1612. Upon the death of the chief minister, Robert Cecil, earl of Salisbury, in May 1612, Carr began to serve as James's secretary.

Meanwhile, he had fallen in love with Frances Howard, wife of Robert Devereux, 3rd earl of Essex. He persuaded James to have a commission annul Frances' marriage, and during these proceedings Frances, probably with Carr's assistance, secretly poisoned Carr's former friend and mentor Sir Thomas Overbury (Overbury, Sir Thomas) (died Sept. 15, 1613), who had opposed the annulment. Carr and Frances were married in December 1613, shortly after Carr had been made earl of Somerset and treasurer of Scotland. He became lord chamberlain in 1614, but in the following year the circumstances of Overbury's death were made public. Somerset and Frances were found guilty of murder; they were imprisoned until 1621 and pardoned fully in 1624. Carr died 21 years later in obscurity.