League of Ireland
Monaghan United were founded in 1979. Among the club's founding members was Sean McCaffrey who was also the manager of the club when they joined the League of Ireland B Division in 1983–84. In 1985–86 Monaghan United became founder members of the League of Ireland First Division. United played eight seasons in the First Division before winning their first promotion. After finishing third in 1992–93 they became the first League of Ireland club to gain promotion via a promotion/relegation play off. They defeated Waterford United 5–2 on aggregate and were subsequently promoted to the 1993–94 Premier Division. They survived just two seasons in the Premier Division before being relegated at the end of the 1994–95 season. Monaghan United gained promotion to the Premier Division for a second time in 2000–01 after finishing second to Dundalk. This time their stay in the Premier Division last just one season. After managing to win just two league games, they finished last and were relegated following the conclusion of the 2001–02 season. Monaghan United reached the final of the 2010 League of Ireland Cup but lost 1–0 in the final to Sligo Rovers. They also finished third in the 2010 First Division and qualified for the promotion/relegation play off. They subsequently beat Waterford United before losing to Bray Wanderers on penalties. In 2011, under the management of Roddy Collins, Monaghan United again qualified for the promotion/relegation play off. This time they won promotion after beating Galway United 5–1 on aggregate. However, midway through the 2012 season, Monaghan United withdrew from the league for "mainly but not only financial" reasons.

Statistics
Stat
Opponent
Score
Season
Date
Record Win
Longford Town
5–0
1992–93
4 October 1992
 
Kildare County
6–1
2009
16 October 2009
 
Salthill Devon
6–1
2010
10 April 2010
Record Defeat
Galway United
0–8
2001–02
26 October 2001
Source:

Dublin Women's Soccer League
Monaghan United formed a ladies football team in 2006. They won Division Four of the Dublin Women's Soccer League in their first season and were promoted to Division Two. In 2007 they again won the league along with the Leinster Junior Cup. In 2008 they won the DWSL Intermediate Cup after defeating Santry 3–1 in the final. In 2012 they reached the semi-finals of the WFAI Intermediate Cup.

Monaghan Cavan League
In 2019, Monaghan United formed a senior team to play in the Monaghan Cavan League First Division. They finished off their debut season by winning the Sean Woods Cup and Jimmy Smith Shield Cup in September 2020, beating Glaslough Villa in both finals.

Ulster Senior League
2021 saw Monaghan United join the Ulster Senior League, the first club from Cavan or Monaghan to do so. In 2022, The Mons decided to withdraw from the league to continue football in the MCL