As a young man he accompanied several diplomatic missions abroad and took part in military expeditions. He was sent to Scotland in February 1587 with certain news of the execution of
Mary, Queen of Scots. He was met at
Berwick-upon-Tweed by the Scottish diplomat
George Young. According to
David Moysie, Young withheld his passport and carried his news to
James VI of Scotland. In 1587, Carey joined in the attempt to relieve
Sluys. In 1588 he served as a volunteer against the
Spanish Armada; so disappointed was he to be left behind by
Drake and Norris the following year that he walked from London to Berwick in twelve days, winning a wager worth two thousand pounds. Carey commanded a regiment in the
Earl of Essex's expedition to
Normandy in support of the Protestant
Henry IV of France in 1591, taking part in the
siege of Rouen. He was knighted by Essex the same year for having by his intercession with the Queen procured his recall. In October 1593 he brought the Scottish rebel
Francis Stewart, 5th Earl of Bothwell, as a guest to
Carlisle Castle. This alarmed his brother-in-law,
Thomas Scrope, who was
Warden of the West March, because
Elizabeth I had declared her nobles would not receive the earl. In the parliaments of 1586 and 1588 he represented
Morpeth; in that of 1593,
Callington; and in those of 1596 and 1601,
Northumberland. From 1592 till the end of Elizabeth's reign he occupied various posts in the government of the Scottish borders, being appointed
Warden of the Middle March in 1596, which he held till February 1598. This was some of the most important work of his life, and he was largely responsible for easing the troubles and the depredations of the
Border Reivers. His conflict with the Scottish
fyrebrande Robert Ker, 1st Earl of Roxburghe was only settled after great skill and tact on Carey's part. In March 1603 he visited the court, and witnessed Queen Elizabeth I's last illness, which he described in his memoirs. Anxious to recommend himself to her successor
James I, and disobeying the orders of the council, he started on horseback immediately after the Queen's death on the morning of 24 March 1603, in order to be the first to communicate the tidings to James. He arrived at
Holyrood late on 26 March. The next day, King James confirmed in a letter to
Robert Cecil that Carey had been first with the news. Carey was appointed a Gentleman of the Bedchamber, but his conduct met with general disapproval and merited censure as "contrary to all decency, good manners and respect," and on James's arrival in England he was dismissed from his new post. Carey went into Scotland again to transact business with
Sir George Home over the ownership of
Norham. He went to
Dunfermline Palace and was the guest of
Alexander Seton who was the guardian of
Prince Charles. Charles had stayed behind in Scotland, partly because he was sickly, and Carey wrote that he was "a very weak child". Prince Charles came south in September 1604 and the king sent Carey to meet him at Bishop's Auckland. On 23 February 1605, he was made governor of Prince Charles. Carey's wife,
Elizabeth Trevanion (not Aletta Hogenhove, who was the wife of his nephew Sir Robert Carey), a lady in waiting to
Anne of Denmark, was responsible for the early training of the weak, stammering Charles. She taught the Prince, a late-developer, to walk and talk at the age of three, and was close to him throughout his life. Upon her husband's accession to the peerage, she became known as Dame Robert Carey, and is said to be the "Old Dame Dob" referred to in the
Jack and Jill nursery rhyme, for her ministrations to the "bruised" King Charles I after his plan to raise revenue by lowering the volume of liquid in the jack (1/2 pint) and gill (1/4 pint) was foiled by publicans by simply making up the difference (up to the 1/2 pint line that is marked by a crown on pint glasses) with water. In 1611, he was made the
Master of the Robes to the Prince, in 1617 his
Chamberlain, and on 6 February 1622, he was created
Baron Carey of Leppington. In 1623 he followed Charles in his visit to
Philip IV of Spain with a
parcel of jewels. Following Charles' succession to the throne he was created
Earl of Monmouth in 1626. In 1621 he sat in Parliament for the last time as MP for
Grampound. He died on 12 April 1639. His eldest son by Elizabeth Trevannion,
Henry Carey, 2nd Earl of Monmouth (1596–1661) succeeded him, and on his death without surviving male issue the peerage became extinct. His
Memoirs were published first by
John Boyle, 5th Earl of Cork in 1759. A second edition, annotated by Sir
Walter Scott, was printed in 1808. A new edition was published in 2005, . ''The Stirring World of Robert Carey: Robert Carey's Memoirs 1577-1625''. ==Family and issue==