Murchad (d. 1042), son of Dúnlaing and overking of Leinster, belonged to the Uí Muiredaig lineage of the Uí Dúnlainge dynasty. His father, Dúnlaing (qv), died at Glendalough in 1014, having held the overkingship of Leinster for only a month. Murchad had nine brothers or half-brothers, of whom two, Donn-cuan (d. 1016) and Augaire (qv), were overkings of Leinster. Another two, Domnall (fl. c.1031) and Dúnchad (blinded 1036), were kings of Uí Muiredaig. He also had three sisters, including Máel-corcra, wife of Amlaíb (Óláfr) son of Sitriuc Silkbeard (qv), the Hiberno-Scandinavian king of Dublin, and Aíbenn, wife of Fergal, king of the Fortuatha of Leinster.
Murchad came to prominence in 1037, after his brother Dúnchad was seized and blinded by Donnchad (qv) son of Gilla-Pátraic, king of Osraige, as that dynasty continued its efforts to gain control of northern Leinster. For his part, Murchad strove to secure Uí Muiredaig as a base from which he could bid for overkingship of the province. He had the support of several local rulers, including his nephew Domnall, son of Aíbenn and Fergal, now king of Fortuatha, and Donnchad son of Áed king of Uí Bairrche. Another of Murchad's brothers, Echdonn, was his tánaise (heir-apparent). In 1039 Murchad's allies slew the local king of Uí Fháeláin, Domnall son of Murchad, and subsequently killed his brother Dúnchad. The removal of these two potential rivals left Murchad as the dominant power in the Kildare–Carlow area.
It seems that by this stage Murchad was regarded as a threat by the emerging Diarmait (qv) son of Donnchad Máel na mBó (qv), king of Uí Chennselaig, who also sought overkingship of Leinster. In 1040 the latter invaded Uí Muiredaig and attacked the ecclesiastical settlements of Castledermot, Moone, Ballaghmoon, and Clonmore, where a cousin of Murchad was abbot. These attacks, however, were repelled. In 1041, Murchad moved to extend his authority within Leinster, dealing ruthlessly with opponents, whether members of Uí Dúnlainge or of rival dynasties. He slew another of his nephews, Gilla-Comgaill son of Donn-cuan, at Kildare, and with the help of the king of Uí Bairrche he captured and blinded Fáelán Ua Mórda king of Loígis. The succeeding ruler of Loígis, described as a grandson of Dúnlaing, was probably a relation and hence an appointee of Murchad.
By this time, if not earlier, Murchad was laying claim to overkingship of Leinster; the regnal lists allow him one year as provincial king. Uí Chennselaig responded by again invading Uí Muiredaig, but this time Murchad overtook them at Cell Mo Lappóc (Kilmalappogue, Co. Carlow), where he defeated and slew Domnall Remur (qv), brother of Diarmait son of Máel na mBó. Seizing the advantage, Murchad allied himself with the overking of Munster, Donnchad (qv) son of Brian, and burned Ferns, the caput of Uí Chennselaig. In revenge, Diarmait sacked Glenn Uissen (Killeshin, Co. Laois) and took several hundred captives. In 1042, Murchad took the field against Diarmait's ally, Gilla-Pátraic son of Gilla-Pátraic king of Osraige, but was defeated and slain, along with his brother Echdonn and their ally, Donnchad son of Áed king of Uí Bairrche, at Mag Muilchet in Co. Laois.
As a result of this battle, Uí Muiredaig was greatly weakened and Uí Dúnlainge was eclipsed as the dominant dynasty of Leinster. Some surviving members of Murchad's immediate family took service with Donnchad son of Brian. For the remainder of the eleventh century the descendants of his brothers Donn-cuan and Tuathal, who took the family name of Ua Tuathail (O'Toole), contested the kingship of Uí Muiredaig with the kinsmen of Máel-mórda (qv) son of Lorcán, who took the family name of Ua Lorcáin (O'Larkin). Not till the twelfth century did Uí Muiredaig re-emerge as a significant political force, and even then they were clearly subject to Uí Chennselaig.