The club was founded in 1948 and was originally called Newcastle United. They were founder members of the Limerick Desmond League in 1955, and were its first champions. In 1985 they became one of the founding members of the League of Ireland First Division, finishing eighth in their first season in the league. The following season the club adopted its current name. During their spell in the League of Ireland, the club twice reached the quarter final of the FAI Cup, in 1988 and 1990. The first occasion was controversial; they faced Cobh Ramblers in the fifth round. The first match was drawn, and Newcastle West won the replay on their own ground 4–2 after extra time. According to the Irish Times' correspondent, "the style they put on in this nail biting thriller that produced four stunning goals in extra time made one wonder just why such a fine football side was having its troubles at league level." However, Cobh's protest, on the grounds that their former player Billy Daly had signed for Newcastle West too late to be eligible to play in the match, was upheld by the Football Association of Ireland, and they were awarded the tie. In response, Newcastle West decided to pull out of the League with immediate effect. After urgent meetings involving all parties, a compromise was reached which saw Newcastle West remain in the league and the cup replay replayed. They beat Cobh 1–0, with Daly scoring the winning goal, but lost to Longford Town in the quarter-final, missing out on a potentially lucrative semi-final meeting with Derry City. In the 1989–90 season, they produced "a shock victory" away to Sligo Rovers in a match where "high-flying tackles and off-the-ball confrontations marred the day", before losing at home in the quarter-final to intermediate club St Francis, who had already knocked out two other League of Ireland clubs in their first FAI Cup campaign. After finishing ninth in the 1989–90 League of Ireland First Division, the club resigned from the league in order to make improvements to their Demesne ground, and were replaced in the league by St James's Gate. They had continued to runa team in the Limerick Desmond League, winning Division One for four consecutive seasons between 1989–90 and 1992–93. They won the league again in 2001–02, by which time Division One had become the Premier Division. Further titles were won in 2005–06, 2007–08, 2008–09 and 2012–13.
