Born in Dublin, Ireland, Treacy started playing football with Belvedere for the youth team, before signing his first professional contract in 2005, keeping him until 2008.
[3] After ending his loan spell at Stockport County, making four appearances, Treacy signed a new contract with the club on 12 June 2007, keeping him until 2011.
[5] It was not until on 31 October 2007 when he made his debut for the club in a League Cup tie against Portsmouth as a substitute, as Blackburn Rovers won 2–1.
"[12] In July 2009, Treacy joined Sheffield United on a six-month loan deal,[13] making his début for the club in a 0–0 draw with Middlesbrough on the first day of the 2009–2010 season.
[14] He soon followed his debut up with two assists for the Blades against Watford the following week and a stunning long range goal three days later in a midweek match against Leicester City.
[15] Since joining the club, Treacy started the season as a regular in the Blades side despite facing an injury that almost saw him sidelined for six months.
[22] After missing two matches due to injury, he returned to the first team against Watford on 3 April 2010, coming on as a 38th-minute substitute, and set up the equalising goal, in a 1–1 draw.
[30] After serving a one match suspension, Treacy returned to the starting line–up against Crystal Palace on 23 October 2010, and "fired home from all of 35 yards for his sixth goal of the season", in a 4–3 win.
[37] Even though Preston North End were relegated to League One, Treacy finished the 2010–11 season with and making forty-one appearances and scoring nine times in all competitions.
Manager Howe expected Treacy to return to Burnley's pre-season training ahead of the 2012–13 season, having given him a second chance in the first team.
[51] Treacy made his first appearance since returning from a loan spell at Sheffield Wednesday, coming on as a substitute for Joseph Mills in the 73rd minute, in a 2–0 loss against Huddersfield Town on 25 August 2012.
[52] However, his poor performance against Plymouth Argyle in the second round of the League Cup led Manager Howe to send him to the club's Development Squad.
[60] After the match, Treacy praised Dyche for putting his career on track and credited the fitness coach Mark Howard for helping him lose weight and improving his physique.
[62] However throughout the 2013–14 season, Treacy's first team was largely restricted to substitute appearances, due to strong competitions in Burnley's midfield positions.
[63] He also faced sidelined, including a suspension following his sending off against West Ham United in the fourth round of the EFL Cup on 29 October 2013, as the club lost 2–0.
Despite keen on signing a contract with the club, Treacy was released by Burnley, having remained a fringe player in the first team squad under managers Eddie Howe and Sean Dyche.
[67] In effort to boost chance to make to the Ireland Squad for UEFA Euro 2012,[68] Treacy joined Sheffield Wednesday on loan until the end of the season.
[69] He made his debut for the club two days later, coming on as a substitute for Jermaine Johnson in the 78th minute, in a 1–0 win over Leyton Orient.
[76] Treacy made his debut for the club in the opening game of the season, coming on as a substitute for Danny Rose in the 66th minute, in a 1–0 loss against Crawley Town.
[80] Treacy returned to Ireland and joined struggling Premier Division side Drogheda United midway through the season.
[85] Treacy left Drogheda United to sign for another Premier Division side, St Patrick's Athletic on a one-year contract.
[89] However due to injuries, Treacy was not in the squad for the League Cup Final as Pats beat Limerick 4–1 to retain the trophy.
[99] However, Treacy suffered a hamstring injury in training ahead of the match and didn't play for the Republic of Ireland U21 for another nine months.
[106] On 24 May 2011, he earned a starting place winning his third cap with an impressive display in the 2011 Nations Cup game against rivals Northern Ireland.
On 12 October 2014, Treacy married his long-term girlfriend in Ireland, causing him to miss the Yorkshire derby against Bradford City.