Fínshnechtae Cetharderc (d. 808), son of Cellach and overking of Leinster, belonged to the Uí Dúnchada lineage of Uí Dúnlainge. His sobriquet, meaning ‘looking four ways’, may be intended to convey a circumspect character; he certainly proved to be a political survivor and did much to strengthen his dynasty's dominance over Kildare. Although he is omitted from the extant pedigrees of Uí Dúnchada, the annals and the Leinster king-list show him to have been a son of Cellach (qv) son of Dúnchad (qv); there is record of three brothers, Fáelán, Muiredach, and Áed, and a sister, Muirenn. His wife is not named, but he had at least two sons, Coscrach and Fáelán. His father died in 776 as overking of Leinster, and was succeeded in turn by two first-cousins, the second of whom, Bran Ardchenn (qv), Fínshnechtae murdered in 795.
Despite the violent way in which he acceded to the kingship, Fínshnechtae does not seem to have encountered much opposition from rival lineages of Uí Dúnlainge. His reign, although interrupted in 805–6, extended over thirteen years. He was, in any case, quite ruthless in dealing with opponents from other dynasties; in 803, presumably to strengthen his dynasty's hold on Kildare, he procured the death of Óengus son of Mugrón, king of Uí Fhailge. Given that Óengus's successor was slain in 806, a year in which Fínshnechtae made a spectacular return to power, it seems likely that the latter was again responsible and was pursuing a policy of repression against Uí Fhailge.
The dynasty of Uí Dúnlainge had long maintained connections with the religious house at Kildare. Fínshnechtae's great-aunt, Condal (qv) daughter of Murchad (qv), had held senior office there, but his immediate family secured an effective monopoly of control. No less than four of his siblings and at least four descendants (direct and collateral) held abbatial office. Fínshnechtae's brother Fáelán attained the abbacy in 798, and in all probability presided over the enshrinement of the relics of St Conláed (qv) at Kildare in 800. Fáelán, styled princeps (royal abbot) in his obit at 804, was succeeded by his two brothers in turn: Muiredach (d. 823) and Áed (d. 829). Meanwhile, Fínshnechtae's sister Muirenn became abbess in 805 and held office till her death in 831. The family's hold on ecclesiastical office at Kildare long outlasted Fínshnechtae; his nephews Artrí (d. 850) son of Fáelán, and Cobthach (d. 869) son of Muiredach, held the abbacy, a role later filled by Fínshnechtae's great-grandson Muiredach (d. 885) son of Bran (qv) (d. 838) son of Fáelán. A grandson named Suibne grandson of Fínshnechtae died (880) as bishop of Kildare. It appears that as Uí Dúnchada asserted its authority in the south Dublin area between the late eighth and early ninth century, there was a parallel extension of the cult of St Brigit (qv) for which Fínshnechtae's family may have been responsible.
During much the same period, an Uí Dúnlainge presence became established at Glendalough. The episode in the Latin Life of St Cóemgen (qv) featuring Fáelán (qv) (d. c.645) son of Colmán probably dates from the end of the eighth century. A late addition in the Book of Leinster (LL 245) claims that Fínshnechtae's father Cellach donated twenty-five ringforts to Cóemgen. It also credits Fínshnechtae himself with unspecified acts of generosity towards the church. It is possible (but by no means certain) that the Glendalough abbot Etarscél (d. 814) son of Cellach was another of Fínshnechtae's brothers.
Perhaps Fínshnechtae's very success at consolidating his dynasty's fortunes within northern Leinster exacerbated Uí Néill anxieties. In 804 the king of Tara, Áed Oirdnide (qv) son of Niall, convened an assembly at Dún Cuair (near Enfield, Co. Meath). Such a development boded ill for Leinster, as Dún Cuair had previously featured as a rendezvous for Uí Néill invasions. In the event, northern Leinster was devastated twice in the months that followed and a submission was extracted from Fínshnechtae. Clearly this arrangement was inadequate from the Uí Néill point of view: in 805 Áed Oirdnide deposed Fínshnechtae and partitioned the Leinster kingship between two dynastic rivals, Muiredach son of Bran of Uí Muiredaig and Muiredach son of Ruaidrí of Uí Fháeláin. At this point, Fínshnechtae went into temporary religious retirement (probably at Kildare) but, within a year, had returned to power – defeating the sons of Ruaidrí, presumably Muiredach and his brother Diarmait, in battle.
Fínshnechtae was not to enjoy his restoration for long; in 808 he died at Kildare of ‘the bloody flux’, as the annalist records. Neither of Fínshnechtae's two recorded sons made much political impact. Coscrach was slain in 815, and Fáelán led an apparently undistinguished career. The kingship passed to the Uí Fháeláin rival, Muiredach son of Ruaidrí, although it would eventually revert to Fínshnechtae's grandson Bran son of Fáelán, from whom the later Uí Dúnchada kings descended.