The English surname of Martin is a variation of the habitational one Marton, from any of several places (principally in Hampshire, Lincolnshire, and Worcestershire, named in Old English as ‘settlement by a lake’, from mere or mær ‘pool’, ‘lake’ + tun ‘settlement’) or as ‘settlement by a boundary’ (from (ge)mære ‘boundary’ + tun ‘settlement’) called firstly Marton and after Martin.Martin Clan

With over 230,000 people holding the surname Martin in France, it is the most common French surname. The origins of its frequency can be attributed to Saint Martin of Tours, who was the most popular French saint, but the reason is not clear.
Martin was never a common given name (Christian name) in the Middle Ages, like Bernard or Thomas (which were later officialized and became common surnames, nowadays ranking second and third respectively). Onomastics have tried to find other reasons for Martin’s popularity, by examining, for example, the repartition of place names, but this explanation also lacks empirical support.
It can be a late surname connected with children of orphanages, like Alexandre, which was never a common first name in the Middle Ages but now appears quite frequently as a surname. Martin can represent charity towards orphans.

Martin exists in Spain, but the more comon form of the name is “Martí.” (The names “Marty” and “Marti” are forms of the name “Martin.”) Jewish families in medieval Spain (Sephardic) Jews who remained in Spain and agreed to accept Christianity were asked to change their surnames. One of the names taken up by these Jewish conversos (originally known in Spain as Marranos, but preferred term is ‘anusim’ which is Hebrew for “forced”) was “Martí”.

See The Mairtine for early Irish beginnings. Later surname variations include Mac Giolla Mhártain, Ó Maol Mhartain, Ó Martain, Ó Máirtín, Mac Máirtín, Mac Máel Martain and were probably distantly related from a Keltoid root stock. Recent DNA evidence has this group in Ireland for 3000 years and aligning with the Ulaidh, Errain, and Eóghanacht in Munster and later in the DalRiata kinship groups.
Echmílid mac Máel Martain was Bishop of Down to 1202. Giolla Ernain Ó Martain, who died in 1218, was an Irish poet and Chief Ollam of Ireland. Fearghal Ó Martain, O.E.S.A., was Bishop of Killala from 1425 to 1432.
After the Norman invasion of Ireland in 1169, numerous new, unrelated bearers of the name from Britain and France, settled in Ireland.
The most well-known Norman family in County Galway were the Martyn family, who were counted among The 13 Tribes of Galway.

There are several groups of Martins or Macmartins in Scotland. The MacMartins of Letterfinlay appear to have allied themselves to the Clan Cameron in the late 14th century, and finally merged with the Camerons after the Battle of Lochaber in 1429. The Martins in Skye are traditionally associated with Clan Donald, and the Lothians were home to a powerful ‘de St Martin’ family from the 12th century. In Ireland there are at least three major families bearing the name “Martin”; one being of foreign origin and the latter two, indigenous Irish clans. There are many mottos and arms registered by various Martins throughout the British Isles. The motto of Abraham Martin of Cleveragh and Bloomfield, County Sligo, was “Hinc Fortior et Clarior”, which translates as: “… hence stronger and more illustrious”. This same motto was registered by another Martin in Edinburgh, 1672.

An Anglo-Norman knight named Robert fitz Martin, born in the late 11th century, settled in England’s West Country, on lands inherited from a grandfather, and later participated in the invasions of Wales, where he was awarded the barony of Cemais, located between Fishguard and Cardigan. Robert fitz Martin established the caput of his barony at Nanhyfer or Nevern. Robert’s son William fitz Robert fitz Martin (born c. 1155) inherited the family’s property and re-established family control over Cemais, which had been lost to the Welsh. The senior line became extinct in 1326, but cadet lines still flourish in England, Wales, Ireland and elsewhere.