Clan Montgomery is one of the oldest Scottish Clans, and its Chronicles are closely interwoven with Scottish history. The progenitors of this Clan were Norman and came from the Castle of Sainte Foy de Montgomery, near Lissieux, Normandy, France. Roger de Montgomery arrived in England with his kinsman, William the Conqueror, in 1066. In 1069 Roger was granted lands on the Welsh border in the County which later took his name, Montgomeryshire. In 1083 he built Shrewsbury Abbey where he is entombed. According to the Doomsday Book, in 1086 he owned 150 castles and lordships within ten counties of England. Roger's grandson Robert de Montgomery, went to Scotland with Walter FitzAlan, also of the Welsh border country, who became High Steward of Scotland and progenitor of the great Stewart Clan. Robert was granted lands by King David I of Scotland in Renfrewshire, and the manor of Eaglesham became the Clan seat of the Montgomerys for many centuries.

From 1165 to 1177 the name of Montgomery is mentioned in many grants and Charters, and the Clan territories expanded considerably. Sir John Montgomery, 7th Chief of the Clan, distinguished himself at the Battle of Otterburn in 1388 when he captured Harry Hotspur, Chief of the Percys. Percy's ransom was to build the Castle of Polnoon for Montgomery. John Montgomery later acquired the baronies of Eglinton and Ardrossan when he married the heiress daughter of Hugh Eglinton. Their grandson, Alexander, was created Lord Montgomery in 1449, and was Governor of Kintrye and Knapdale. Hugh, 3rd Lord Montgomery, was created Earl of Eglinton in 1507.

Although the Clan in general embraced the new faith when it arrived in Scotland, Hugh, the Earl's son, remained Catholic and was a staunch supporter of Mary Queen of Scots. He was taken prisoner at the Battle of Langside in 1568 while defending the Queen in her last battle. Ironically, his daughter married the Earl of Winton and their son, Alexander, 6th Earl of Eglinton and Chief of the Clan Montgomery, was a staunch Presbyterian who fought for the convenators in the Wars of Charles I. Alexander's son, George, started the branch of Montgomerys at Skelmorlie.

There were many branches of the Clan Montgomery. Hugh Montgomery of Hassilhead Castle had a substantial branch of the Clan in his territories. Viscount Montgomery of the Great Ardes in Ireland was descended from an uncle of John Montgomery, the first Lord of Eglinton.

The Chiefship passed to the Montgomerys of Coilsfield who were, according to Robert Burns, "a martial race, bold, soldier featured and undismay'd". The Chief was also the Lord Lieutenant of Ireland. At the end of the 16th century, Lady Montgomery of Eglinton set up linen and woolen manufacturing mills for the weaving of the tartan in Northern Ireland which were largely staffed by Montgomery clansmen. One of the greatest Scottish poets, Alexander Montgomerie was the court poet (Poet Laureate) of King James Vl, and was of the branch from Hassilbead Castle. His allegorical poem, "The Cherrie and the Slae" appeared in 1597 and "Declare, ye banks of Helicon" in 1621. The Montgomerys organized one of the earliest world gatherings for a Scottish Clan in the form of the "Eglinton Tournament" in 1839. It was the forerunner of later gatherings and festivals and set the pattern and style of the Edinburgh Festival. The Montgomery Clan produced the late Viscount Field Marshall Montgomery, the great tactician of the Second World War.

One of the first Montgomerys to settle in North America was a Chieftain, Hugh, who settled in New Jersey in 1680. A chieftain of the Irish branch from Londonderry settled in New Hampshire in 1719. The economic depression which descended over Scotland in the 18th and 19th centuries found many clansmen looking toward the New World for their future. They sailed aboard the armada of tall ships which plied the North Atlantic and pioneered settlements in North America. A significant role in the development of the United States was the 77th Highland Regiment which was formed in 1757 by Archibald Montgomery, Chief of the Clan, and which included many clansmen. Their exploits in the campaign against the French are legend, and it was this regiment, under General Forbes, which renamed modern Pittsburgh. General Richard Montgomery was killed in the storming of Quebec on December 31, 1775. He was the first American general to die in the Revolution. He became a symbol of all that was finest in the leaders of the American Revolution. Many of the "Montgomery" place names which dot the nation honor his memory.