At the Synods of Rathbreasail (1111) and Kells/Mellifont (1152) the diocesan boundaries were formalised. Over the succeeding decades the boundaries of the Diocese of Clogher were settled, eventually embracing the territorial lordships of the MacMahon and Maguire clans.
Up to October 1542, the pre-Reformation Episcopal succession is shared with the Church of Ireland (Anglican) tradition.
The following is the Episcopal succession for the Roman Catholic Diocese of Clogher
| Cináeth Ua Baígill | – 1135 |
| Gilla Críst Ua Morgair | 1135 – 1138 |
| Áed Ua Cáellaide | 1138 – 1178 |
| Mael Ísu Ua Cerbaill | 1178 – 1186 |
| Gilla Críst Ua Mucaráin | 1187 – 1193 |
| Máel Ísu Ua Máel Chiaráin | 1194 – 1197 |
| Gilla Tigernaig Mac Gilla Rónáin | 1197 – 1218 |
| Donatus Ó Fidabra | 1218 – 1227 |
| Nehemias Ó Brácáin | 1227 – 1240 |
| David Ó Brácáin | 1245 – 1267 |
| Michael Mac an tSáir | 1268 – 1287 |
| Matthaeus Mac Cathasaig I | 1287 – 1310 |
| Henricus | 1310 – c.1316 |
| Gelasius alias Cornelius Ó Bánáin | 1316 – 1319 |
| Nicolaus Mac Cathasaigh | 1320 – 1356 |
| Brian Mac Cathmhaoil | 1356 – 1358 |
| Matthaeus Mac Cathasaigh II | c.1361 – |
| Aodh Ó hEóthaigh (alias Ó Neill) | – 1369 |
| Johannes Ó Corcráin | 1373 – c.1389 |
| Art Mac Cathmhaoil | 1390 – 1432 |
| Piaras Mag Uidhir | 1433 – 1447 |
| Rossa mac Tomáis Óig Mág Uidhir | 1450 – 1483 |
| John Edmund de Courcy | 1484 – 1494 |
| Andreas | 1500 – |
| Nehemias Ó Cluainín | 1502 – 1503 |
| Giolla Pádraig Ó Condálaigh | 1504 – 1504 |
| Eoghan Mac Cathmhaoil | 1505 – 1515 |
| Pádraig Ó Cuilín | 1517 – 1534 |
| Hugh O’Carolan | 1537 – 1569 |
| Raymond MacMahon | 1546 – 1560 |
| Cornelius MacArdel | 1560 – c.1592 |
| Eugene Matthews | 1609 – 1611 |
| Heber MacMahon | 1643 – 1650 |
| Patrick Duffy | 1671 – 1675 |
| Patrick Tyrrell | 1676 – 1689 |
| Hugh MacMahon | 1707 – 1715 |
| Bernard MacMahon | 1718 – 1737 |
| Ross MacMahon | 1738 – 1747 |
| Daniel O’Reilly | 1747 – 1778 |
| Hugh O’Reilly | 1778 – 1801 |
| James Murphy | 1801 – 1824 |
| Edward Kernan | 1824 – 1844 |
| Charles MacNally | 1844 – 1864 |
| James Donnelly | 1865 – 1893 |
| Richard Owens | 1894 – 1909 |
| Patrick McKenna | 1909 – 1942 |
| Eugene O’Callaghan | 1943 – 1969 |
| Patrick Mulligan | 1970 – 1979 |
| Joseph Duffy | 1979 – 2010 |
| Liam S. MacDaid | 2010- 2016 |
| Lawrence Duffy | 2019- |
