In 1582, Lord Seton, as he then was, married Lady Margaret Montgomerie, oldest daughter of Hugh, third Earl of Eglinton, by whom he had five sons and a daughter.

His son and Heir, Robert, became 2nd Earl of Winton, but resigned the title to his brother George, who was the celebrated 3rd Earl of Winton

His 3rd son, Sir Alexander Seton of Foulstruther,  succeeded as sixth Earl of Eglinton by right of descent from his mother and which arrangement was negotiated with the Earl of Eglinton to continue the line in bearing the name of Montgomerie, and in descent from whom is the present Earl of Eglinton and Winton, Lord Montgomerie, Ardrossan, Baron Seton and Tranent, etc.

On the death of his father, George, seventh Lord Seton, in 1585, Robert succeeded as eighth Lord Seton.  Although his father left the estates heavily encumbered by reason of the great expense of several embassies and of his losses suffered by adhering to the Queen’s party, yet by prudence and ability he was soon able to put his affairs in good condition and provide both sons and daughters with respectable fortunes.  “He was very hospitable, and kept a noble house, the king and queen being frequently there, and all French and other ambassadors and strangers of quality were nobly entertained.”  He was a favorite with the king, and was created Earl of Winton with solemnity and pomp of banners, standards, and pennons, inscribed with loyal mottos and quaint devices at Holyrood House, on the 16^th of November, 1600.  He was a great builder and a wise improver of his property, especially by working on the old harbor of Cockenzie, along the Firth of Forth, a curious fishing village of great antiquity whose history is little known.  It originally sheltered only small boats, but when improved by art and accommodated vessels of a larger size.  In January, 1599, the king granted him a charter under the Great Seal of Scotland concerning Cockenzie.