The 33-year-old Bellewstown-born centre-cum-wing made his Leinster debut against Ulster in August, 1998 and his Heineken Cup debut a month later in a 33-27 win over Llanelli at Stradey Park. He went on to make 87 appearances in Europe, scoring 27 tries and 138 points.
Having started his career at centre, his two Heineken Cup final appearances were both on the wing and he also helped Leinster clinch the Celtic League titles in 2002 and 2008. He scored 21 tries in 65 appearances for Ireland, helping them to win three Triple Crowns, and won three Test caps for the British & Irish Lions on their 2005 tour to New Zealand.
"Every professional sportsman realises that at some point their career will come to an end. I have been extremely fortunate to have played regularly for my province and with Ireland since my debut with Leinster in 1998 and. while I am disappointed that injury has forced me to retire now, I know I have been very lucky to have had such a long and largely injury-free career," said Horgan.
"It has been a tremendous honour to represent my province and my country. When you first start playing sport that is the ultimate ambition but few people are lucky enough to realise it. I am just so grateful that I was given that opportunity.
"I am equally fortunate to have played at a time when Leinster and Ireland experienced such great success and alongside a group of players with unprecedented talent and ambition. To perform at the top of any professional sport players need good coaches and Ireland has been well served during my time with the National squad.
"At Leinster, to have played under Mike Ruddock, Matt Williams, Michael Cheika and, as it turned out for the last season of my career, Joe Schmidt, represents the kind of good fortune that only 'lucky' players get. My final expression of thanks is to the supporters of both Ireland and Leinster with whom I have shared some special days that I will never forget."
Horgan leaves the game with Leinster ready to defend their Heineken Cup title against Carediff Blues at the Aviva Stadium on Saturday, 7 April, and sitting on top of the RaboDirect PRO12. He is the fourth highest try scorer in Heineken Cup history with 27 - Vincent Clerc 32, Brian O'Driscoll 30, Dafydd James 29 - and his 87 matches in the tournament is the most by a Leinster player and the fourth highest of all-time.
"As one of the longest serving players in the professional age, Shane will no doubt go down as one of the greats of Leinster and Irish rugby. He was a strong leader within the group whose contribution off the field mirrored his many feats on it," said Leinster coach Joe Schmidt.
"It was great to be involved with Shane last season where his performances contributed so much to the success of the team. It was fitting that his final season culminated in a second Heineken Cup success.
"The last year has been a frustrating one for him with knee surgery and long periods of rehabilitation. Unfortunately, despite his best efforts, he has been unable to regain full fitness. It is a testament to Shane that his professionalism and influence have continued to impact positively on the group during this season.
"A born winner and resilient competitor, Shane's retirement will no doubt leave a void in the group, but I know that his legacy of excellence and athleticism will continue to inspire future generations and we wish him all the best in the future."
DOB: 18 July, 1978 - Bellewstown, Co. Meath
Ht: 1.93m / 6' 4"
Wt: 104 kg / 16st 5lb
Position: Centre / Wing
Leinster: 207 apps / 71 tries, 1 dg
Ireland: 65 caps / 21 tries
British & Irish Lions: 3 caps / 1 try
Heineken Cup: 87 apps / 27 tries, 1dg
Honours: 3 Triple Crowns, 2 Heineken Cups, 2 Celtic Leagues