In his playing career he was nicknamed "King Henry" because of his directive style, dominance, competitive spirit, and leadership on the field.

[4][5][6] Raised in Ballyhale, County Kilkenny, Shefflin served an obligatory but underrated hurling apprenticeship at St Kieran's College.

He joined the Ballyhale Shamrocks senior team as a goalkeeper at the age of 17 in 1996 and spent the next 21 years as one of the club's key outfield players.

Shefflin was educated at St Patrick's national school in Ballyhale where his hurling skills were first noted and honed by the local headmaster, Joe Dunphy.

Shefflin later attended St Kieran's College in Kilkenny, before studying electronics at the Waterford Institute of Technology (WIT).

[17] His main area of responsibility is in the agri-business side of matters, handling the finance for all the New Holland tractor sales in the locality.

[21] During his schooling at St Kieran's College in Kilkenny, Shefflin established himself as a key member of the senior hurling team.

[25] He later added a Leinster medal to his collection when Ballyhale secured a comprehensive 1–20 to 1–8 defeat of Birr to take the provincial title for the first time in seventeen years.

[31] The subsequent provincial decider saw Ballyhale hit fifteen wides, however, Shefflin still collected a third Leinster medal following a 1–16 to 1–8 defeat of Tullamore.

[33] Five-in-a-row proved beyond Ballyhale Shamrocks, however, the team bounced back in 2012 having lost the championship decider the previous year.

Shefflin won his first National Hurling League medal, as a late Brian Dowling free secured a narrow 2–15 to 2–14 victory over Cork.

[47] After facing a shock, last-minute 2–15 to 1–16 defeat by Wexford in the Leinster semi-final in 2004, Kilkenny worked their way through the qualifiers and lined out against Cork in the All-Ireland decider on 12 September 2004.

[48] The game was expected to be a classic, however, a rain-soaked day made conditions difficult as Kilkenny aimed to secure a third successive championship.

On 3 September 2006 Kilkenny faced a Cork team who were presented with the opportunity to become the first side in nearly thirty years to secure three successive All-Ireland championships.

[57] On 2 September 2007 Kilkenny faced defeated Munster finalists and surprise All-Ireland semi-final winners Limerick in the championship decider.

In spite of losing their captain and star player, Kilkenny still went on to win the game by 2–19 to 1–15 and Shefflin had the honour of collecting a fifth All-Ireland medal and receiving the Liam MacCarthy Cup.

A 23-point winning margin, 3–24 from play, only two wides in the entire match and eight scorers in all with Eddie Brennan and Shefflin leading the way in a 3–30 to 1–13 victory.

[64] On 6 September Kilkenny were poised to become the second team ever in the history of hurling to win four successive All-Ireland championships when they faced Tipperary in the decider.

For long periods Tipp looked the likely winners, however, late goals from Shefflin (penalty) and substitute Martin Comerford finally killed off their efforts to secure a 2–22 to 0–23 victory.

[67] While it was feared that this would rule him out of the All-Ireland decider against Tipperary on 5 September, he made a remarkable recovery and was deemed to fit to start that game.

Galway stunned the reigning champions with two first-half goals, however, Kilkenny's championship debutant Walter Walsh gave a man of the match performance, claiming a 1–3 haul.

[87] Shefflin subsequently secured a thirteenth Leinster medal, as a dominant Kilkenny display gave "the Cats" a 0–14 to 1–9 defeat of Dublin.

After stating in November 2014 that he intended to make a decision after the conclusion of the All-Ireland series of the club championship, Shefflin called a press conference on 25 March 2015 and announced that he was retiring from inter-county hurling.

In a statement he said, "When I reflect back over the past 16 years playing the game that I love, at the highest level with Kilkenny, it is impossible to quantify the endless hours of happiness, satisfaction and fulfilment I have enjoyed.

"[91][92] In 2015, Shefflin joined The Sunday Game as an analyst for their coverage of the 2015 All-Ireland Senior Hurling Championship and featured on RTÉ Radio 1.

The game ended in somewhat controversial circumstances when the referee awarded a free when Munster's Peter Queally was deemed to have fouled Jimmy Coogan.

"[97] Six-time All-Ireland dual medallist and All-Ireland-winning manager Jimmy Barry-Murphy wrote: "He is most certainly the greatest hurler that I have ever seen, and I even saw Christy Ring towards the end of his days.

"[98] Writing in the Kilkenny GAA Yearbook 2012, contemporary Cork hurler, Donal Óg Cusack, wrote: "If there is better to come than Henry, I for one would hope to be around to see him.

Henry is simply irreplaceable and the measure of the man is his ability to bounce back from serious injuries in recent years to get himself fully fit for the championship.

[105] On 12 December 2017 it was announced that Shefflin would act as co-manager of the Ballyhale Shamrocks senior team alongside his brother Tommy.