Boyce began his career at Cliftonville, scoring 19 goals in his debut season. He won the IFA Premiership Player of the Month Award for April 2010, and was named the Northern Ireland Football Writers' Player of the Year for the 2009–10 season. Boyce is from the Lower Falls in Belfast. He played for Immaculata for most of his youth years, during this time he attended St Joseph's Primary School Slate Street and St Mary's Grammar School, located on the Glen Road in Belfast, he spent all his secondary school years there and went on to study A Levels.
As his ability and skills in his football career developed he was spotted by Cliftonville, and they signed him. He spent his first year there playing in the reserves but in the 2009–10 season, Boyce became a first team regular.
Boyce went on trial with Scottish club Celtic in July 2010, and then held discussions in mid-August 2010 about a move to German club SpVgg Greuther Fürth. However, the move collapsed a few days later.
Boyce eventually signed for another German club, Werder Bremen, on 31 August 2010. He was released by the German club in October 2011, having only made three appearances for the club's reserves side.
Boyce rejoined Cliftonville in January 2012. In the 2012–13 season, he helped Cliftonville win the league title for the first time since 1998, finishing as the league's top scorer with 29 league goals. He was also named as the 2012–13 Ulster Footballer of the Year and Northern Ireland Football Writers' Player of the Year. He won a second league title with the north Belfast club in 2013–14, scoring another 21 league goals before, in July 2014, the club announced that it had withdrawn its offer of a new contract to Boyce.
On 13 June 2014, it was announced Boyce had signed a pre-contract with Ross County. On 13 April 2015, Boyce scored County's first ever top-flight hat-trick in a 3–0 win at St Mirren. He then enjoyed a prolific season in 2015/16, scoring 17 goals in 24 games. Boyce signed a new contract with County in February 2016. He was the top goalscorer in the 2016–17 Scottish Premiership, with 23 goals.
On 20 June 2017, Boyce became a club record signing for EFL Championship side Burton Albion, agreeing a three-year contract with the club. Just weeks later, however, Boyce suffered a serious knee injury that will keep him out of action for most of the 2017–18 season.
Boyce was selected to play for the Northern Ireland national under-21 football team. On 31 January 2011, Liam Boyce received his first senior call-up to the Northern Ireland squad to appear in the Nations Cup. This call-up came after his move to German club Werder Bremen in September 2010. On 9 February 2011, Boyce made his debut against Scotland in which he came on as a 72nd-minute substitute for Niall McGinn. He received his second call-up for Northern Ireland's Group C clash with Serbia in Belgrade on 25 March 2011.
On 2 June 2017, Boyce scored his first goal for Northern Ireland in a 1–0 friendly victory over New Zealand at Windsor Park.As of 28 May 2017
Scores and results list Northern Ireland's goal tally first.
CliftonvilleIrish Premiership: 2012–13, 2013–14
Irish League Cup: 2012–13, 2013–14
County Antrim Shield: 2008–09, 2011–12
Ross CountyScottish League Cup: 2015–16