Mac Flainn, Flann (Florence, Florentius) (d. 1256), archbishop of Tuam, belonged to a Connacht ecclesiastical lineage that was apparently associated with Clonfert. Other members of his family who held senior church office included a later archbishop of Tuam, Nicol Mac Flainn (d. 1286). Flann was a papal sub-deacon, and served as chancellor of Tuam. On 27 May 1250 he was elected to the archbishopric after the death (c. Christmas 1249) of Máel-Muire Ua Lachtáin. His election received assent from the English crown and he was granted custody of the temporalities (25 July 1250); however, the procedure of his election had been uncanonical, so he travelled to Rome to plead his case. He was provided to the see by the pope, and was consecrated archbishop on Christmas day 1250.
During his first year in office he convened a synod at Tuam. An acclaimed scholar himself (his obit praises his wisdom, learning, and knowledge of law), Flann built a house for scholars at the Dominican priory of Athenry, and apparently bequeathed books on canon law to the friars there. However, his relatively short episcopate was otherwise marked by conflict with his suffragans and his ecclesiastical tenants, with the primatial see, and with the English crown – although he was perfectly willing to make use of English law when it suited his purposes.
Within his own province, he reopened a dispute – initiated by his predecessors – to obtain possession of Annaghdown (Co. Galway), a breakaway diocese which, although held by a native Irish bishop, Conchobar, enjoyed English support because the alternative for the Galway colony was ecclesiastical control by Tuam. Flann pleaded with King Henry III and, having apparently conceded rights for the building of a castle at Annaghdown, was granted the temporalities of that diocese on 30 July 1253 and later obtained papal confirmation of the see. He also quarrelled with Tomás Ó Maicín, bishop-elect of Achonry, in 1251, and with Tomás Ó Cuinn, bishop of Clonmacnoise in 1255, on the matter of revenues. In contesting the tenure of certain ecclesiastical properties by Ó Maicín and by one Matthew Mac Giollarotha, Flann appealed to the English king's justices in Ireland, who secured a mandate to proceed against the defendants.
A case in which he supported a suffragan is that of Seoán Ó Laidig, OP, bishop of Killala, whose election was apparently irregular and who had been ordered to resign by Pope Urban. Flann's backing of Ó Laidig, in defiance of the pope and of an episcopal commission which included another of his suffragans, Tommaltach Ua Conchobair of Elphin, ensured the survival of that beleaguered bishop, who remained in office till 1264. The insubordinate and generally uncooperative attitude of Flann can hardly have helped relationships with the primatial see of Armagh; a more specific issue was his resistance to visitation by the primate. In 1255 Pope Alexander IV ordered Tuam to allow quinquennial visitations by Armagh. Meanwhile, Flann became increasingly angered by what he viewed as an undermining by English officials of the church's autonomy in legal matters, with disputes between bishops and their tenants being resolved by secular courts. That same year, he travelled to England to state his grievances to King Henry III, who gave general assurances regarding the welfare of the church. Back in Tuam, it appeared to Flann that no change of policy was being implemented.
He undertook another journey to England with a further petition in May 1256, but died at Bristol before 29 June, on which date leave to elect a successor was issued. His immediate successor, Walter de Salerno, dean of St Paul's, London, was provided by the pope on 29 May 1257, but died within a year (22 April 1258). Tommaltach Ua Conchobair, bishop of Elphin, was then elected to the vacant see.