Waterford United Maguire started his career at
Waterford United, making his debut in July 2011 against
Mervue United. During his career at Waterford he scored 14 goals in 32 games. Waterford's chairman, John O'Sullivan said of Maguire, "I'm a great fan of
Lionel Messi at Barcelona. When I look at Seanie, he really reminds me of him."
West Ham United In January 2013 Maguire signed for
West Ham United on a two-and-a-half-year contract. He was released by West Ham at the end of the
2014–15 season.
Sligo Rovers loan In February 2014 Maguire signed on loan for
Sligo Rovers. Maguire made his debut for Sligo on 24 February in a 4–1 away win in the
Setanta Cup against
Crusaders. His only goal for the club came on 27 July in a 2–0 home win against
Limerick The loan period which lasted until August 2014 and included two
Europa League qualifying games against
Rosenborg.
Accrington Stanley loan In September 2014, Maguire joined
Accrington Stanley on loan, making his football league debut against
Northampton Town on 20 September, scoring his first goal and Accrington's fifth in a 5–4 victory. In December 2014, Maguire returned to West Ham at the end of the loan. He had scored four goals in 13 games. On 24 December, although his return to West Ham had been announced, Accrington extended his loan until 18 January 2015.
Cork City After half a season at
Dundalk, where he won a Leinster Senior Cup medal but did not make the matchday squad for the FAI Cup Final, Maguire signed for
Cork City on 9 December 2015. On 27 February Maguire scored in his first competitive game for City, in the
2016 President's Cup final against former club
Dundalk. A week later, Maguire scored twice in a 2–0 win over
Bohemians on his league debut for Cork. He finished the season as the
league's top scorer with 18 goals, and he also scored the late winner as Cork beat Dundalk 1–0 in the
FAI Cup. On 3 June 2017, it was reported that Maguire had agreed a transfer to
Preston North End by the end of July 2017. On 6 July 2017, Maguire scored a hat-trick against
Levadia Tallinn in the second leg of their first qualifying round of the
2017–18 UEFA Europa League at
Turners Cross to become Cork City's leading goalscorer in European competition.
Preston North End On 3 June 2017, Cork and Preston agreed a deal for Maguire to join Preston at the end of July. He signed a three-year deal with the club, with
Cork City describing the fee as "an appropriate but undisclosed compensation package." Maguire made his competitive debut for Preston on the opening day of the
Championship season, playing 74 minutes before being substituted, against
Sheffield Wednesday. His first competitive goal for Preston came against
Barnsley on 9 September. Maguire returned from a hamstring injury in March to score two goals off the bench as Preston beat
Bolton Wanderers 3–1 on 3 March. He continued his comeback from injury with another goal from the bench against
Bristol City as he netted the winner in a 2–1 win at
Deepdale Stadium.
Coventry City On 26 January 2023, with his North End contract set to expire at the end of the season, Maguire left Deepdale to sign for fellow Championship club
Coventry City on a permanent deal until the end of the season.
Carlisle United On 29 July 2023, Maguire signed a one-year contract with
EFL League One club
Carlisle United. He was released when his contract expired.
Return to Cork City On 6 August 2024, when the club were competing in the
2024 League of Ireland First Division, Maguire returned to
Cork City on a multi-year contract. On 6 September 2024, he was part of the side that defeated
UCD 1–0 at the
UCD Bowl to win promotion by winning the
2024 League of Ireland First Division. On 3 October 2025, Maguire opened the scoring in his side's
FAI Cup Semi Final win over
St Patrick's Athletic to help earn his side a place in the final. Maguire scored 5 goals in 24 games in the league in 2025 as his side finished bottom of the table and were relegated back to the First Division. On 9 November 2025, he was part of the starting 11 in the
2025 FAI Cup final as his side were beaten 2–0 by
Shamrock Rovers at the
Aviva Stadium. Following the club's relegation, Maguire drew interest from
Shamrock Rovers,
Derry City and
Bohemians ahead of the 2026 season, but Cork City informed the clubs and Maguire that he was not for sale, with his contract running until the end of 2027. In February 2026, he extended his contract with the club by a further season, until the end of 2028. ==International career==