Academy Sheppard initially played for Portmarnock AFC and Shelbourne before moving to the
Everton Academy.
Galway United In February 2010 Sheppard signed for
Galway United, and made his
League of Ireland debut at
Richmond Park on the opening day of the
2010 League of Ireland season. His goal scoring in April earned him the Airtricity SWAI Player of the Month Award. In his last game for the club, he scored the winner in the Premier Division promotion/relegation play-off.
Shamrock Rovers In January 2011, Sheppard signed for the League of Ireland Champions. He picked up his first senior trophy, playing all five games and scoring three goals en route to winning the
2011 Setanta Sports Cup. In August 2011, Sheppard helped Shamrock Rovers make history in becoming the first ever League of Ireland team to reach the group stages of a major European club competition when they qualified for the
2011-12 UEFA Europa League group stage. Sheppard earned the penalty late in extra time that saw Rovers win through 3–2 on aggregate away to
FK Partizan in the
2011 Europa League Playoff Round. In October he scored at
PAOK in the Europa League group stage. He scored a total of 15 goals in 35 appearances in the
2011 Shamrock Rovers F.C. season.
Reading On 12 January 2012, Sheppard announced via Twitter that he had signed a two-and-a-half-year contract at
Reading, leaving Shamrock Rovers on a free transfer. Reading reportedly beat off interest from other
Championship clubs including
Blackpool,
Cardiff and
Peterborough United.
Accrington Stanley Loan On 4 August 2012, Reading announced that Sheppard was joining
Accrington Stanley on a six-month loan deal. He made his debut in their 1–0
League Cup defeat against
Carlisle United on 11 August and then scored the winner against
Southend United a week later, his first goal in English football. He returned to Reading on 3 January 2013 having not featured for Accrington since mid October.
Return to Shamrock Rovers On 31 January 2013, he re-joined Shamrock Rovers on a six-month loan deal. He made his return to the team in a 1–0 defeat to
Coleraine on 11 February in the
Setanta Cup, but had to wait nearly three months for his first goal, scoring a late equaliser in a 1–1 draw with
Sligo Rovers on 3 May. Days before his original spell was due to expire, Sheppard's loan was extended until the end of the
2013 League of Ireland season. In December 2013 Sheppard signed a one-year contract with Shamrock Rovers for the 2014 season after leaving Reading without making an appearance.
Cork City On 1 November 2014,
Cork City announced the signing of Karl Sheppard from
Shamrock Rovers. Sheppard scored 2 goals in his first 2 games for the Leesiders. In August 2015, it was announced that Sheppard had signed a 2-year contract to keep him at City, and he went on to score
13 goals in the 2015 season. He scored his second European goal against
FCI Levadia Tallinn in the
2017–18 UEFA Europa League A member of the FAI Cup and Premier Division double winning squad in 2017, by the start of the 2018 season Sheppard had scored 30 goals from 92 league appearances across 3 seasons (2015/2016/2017) with Cork City.
Shelbourne On 6 November 2019
Shelbourne announced the signing of Sheppard following his departure from
Cork City. The season ended in disappointment for Sheppard and Shelbourne, as the club were relegated back to the
League of Ireland First Division while Sheppard failed to score in his 13 appearances in all competitions over the season. On the 17th January 2021, Sheppard announced his retirement from the game aged just 29, with
Arthritis struggles cited as his reason for the decision. ==International career==