Mullan, together with its variants Mullin, Mullen, Mullane McMullan and Mullins, can have a variety of distinct origins. First, it may be the anglicisation of the Irish name Ó Maoláin, from a diminutive of maol, "bald" or "tonsured", which arose separately in a number of areas. The Co. Galway family of the name claim descent from Maolán, himself descended from a King of Connacht. A different family of the same name were based in the Keenaght district of Co. Derry, having originally lived in the Laggan district of Donegal, and were followers of the O'Cahans. In Co. Monaghan a family of the name arose around the modern town of Clones; their name has also been anglicised as Mollins. In nearby Tyrone, the Ó Mealláin, more accurately anglicised as O’Mellan or Mellon, have become Mullans in many instances, no doubt because of the numerical superiority and resultant familiarity of the latter. Yet another family hails from south Co. Cork, where the name is frequently given as Mullins. As well as all of these, many MacMillans, Scottish settlers in Ulster in the seventeenth century, adopted MacMullan, often shortened to Mullan. There is also an English name Mullins, from the Middle English miln, "mill", and a good number of Irish bearers of the name are undoubtedly of this origin.

Alan Mullan (d.1690) was a well-known anatomist who discovered the circulatory system of the eye when he dissected an elephant in 1681.

Shane Crosagh O’Mullan, of the Derry family, lost his property in 1729 and subsequently became a notorious outlaw, or rapparee. he eventually captured and hanged, along with his 2 sons, at Derry.

Karl Mullen (1926 - ), of the Munster family, was one of Ireland’s best rugby players. He captained the Irish team to its only Grand Slam in 1948.

Mullin households by county in the Primary Valuation property survey of 1848-64.
Click on a county name for a parish breakdown(paying).
Antrim 5
Armagh 10
Belfast city 6
Carlow 2
Cavan 9
Clare 2
Cork 4
Cork city 2
Derry 27
Donegal 8
Down 3
Dublin 2
Dublin city 2
Galway 72
Kildare 2
Kilkenny 1
Laois 6
Leitrim 2
Limerick city 3
Longford 5
Louth 15
Mayo 27
Meath 5
Monaghan 6
Offaly 2
Roscommon 11
Sligo 12
Tipperary 3
Tyrone 52
Waterford 2
Westmeath 5
Wicklow 1