Roger de Montgomery called "The Great" was father to another Roger, born about 1030 who was joint Regent of Normandy when William the Conqueror invaded England in 1066. He followed King William to England where he was created Earl of Arundel, he was later made Earl of Shropshire or Shrewsbury and the county of Montgomery is named after him. The first of the family in Scotland was Robert de Montgomerie who obtained a grant of the lands of Eaglesham in Renfrewshire, for some time the principal home of the Montgomeries. His descendant John Montgomerie of Eaglesham was the distinguished warrior who captured Henry Percy called Hotspur at the Battle of Otterburn in 1388. With Percy's ransom he built the castle of Polnoon as well as acquiring Eglinton and Ardrossan through his marriage to Elizabeth of Eglinton.

His grandson, Sir Alexander was created Lord Montgomerie and became a member of the King's council. Hugh, the 3rd Lord Montgomerie was created Earl of Eglinton in 1507. He was amongst those who opposed James III and fought at Sauchieburn in 1488, where the king lost his life. He also received the Isle of Arran with the custody of Brodick Castle. The 2nd Earl remained a devout Catholic at the Reformation and fought on the side of Mary Queen of Scots at her final defeat at Langside in 1568. He was declared guilty of treason and imprisoned in Doune Castle. When he was released he tried to secure the safety and toleration of Catholics in the wake of the Reformation.

Ironically his daughter Lady Margaret married Robert Seton, 1st Earl of Winton, a loyal Covenantor in the wars of Charles I and it was their son, Alexander Seton who took the name Montgomerie who became the 6th Earl of Eglinton. He was also a Presbyterian supporter and followed Charles II. He was imprisoned for his Royalist sympathies by General Monk in 1659 after the death of Cromwell however in the following year it was Monk himself who restored the monarch to his throne. The 9th Earl was one of the Privy Council of King William and later Queen Anne and during the rebellion of 1715 actively promoted the training of the fencible men of Ayrshire. The 11th Earl raised the 77th Foot Highlanders.  The 13th Earl was renowned for his celebrated tournament at Eglinton Castle in 1839. The Montgomeries and the Cunninghams had one of the longest running feuds in Scotland; in the 16th century Eglinton House was burnt and the 4th Earl was killed by Cunninghams, finally it was resolved by the government.