O'Herlihy was a Starfleet ensign serving on the USS Enterprise. O'Herlihy was one of three tactical officers who were part of the landing party that beamed down to the observation post on Cestus III in 2267. Arriving, they discovered that the colony had been destroyed. Shortly after their arrival, the landing party came under attack from Gorn soldiers. O'Herlihy was killed by disruptor fire, seconds after discovering the position of the attackers.