As outgoing senator Dr Mary Henry was re-elected to the Seanad on the Trinity College panel, defeated candidate Professor Ivana Bacik lodged an official complaint about the college's election register.
Prof Bacik said the college had used the 2001 register of graduates as the electorate, rather than the current register and that this disenfranchised some 2,000 new graduates.
The college defended the use of the old register as correct and the deputy returning officer, Mr Dermot Sherlock, said they had received legal opinion on the issue.
Senator Henry beat Prof Bacik by 879 votes on the 10th count and joins outgoing Senators David Norris and Shane Ross, both of whom were re-elected earlier in the count.
The final count was based on the distribution of the votes of Dr Sean Barrett, an economist and senior lecturer in Trinity. He was "not personally disappointed but disappointed that two-thirds of the electorate did not vote".
Senator Henry's campaign cost between €10,000 and €14,000. She also thought the current register would be used but was pleased at the result, particularly in the light of the "hot competition" from Prof Bacik and the disability and Travellers' rights compaigner, Ms Rosaleen McDonagh.
Prof Bacik, Reid professor of criminal law in Trinity, stressed that she would "not be challenging the result" of the election.
The 34-year-old candidate, whose campaign cost about €3,500, said the new register came into effect on June 1st. Trinity College had used May 17th, the closing day for nominations, as the cut-off point and the 2001 register was in place at that time.
