Dubliner Shane Jennings has made 118 Leinster appearances over two spells since making his debut in the 2002/03 season. The St. Mary's College clubman also featured in the 2008/09 Heineken Cup winning side.
The 29-year-old flanker has played in 15 matches for Leinster this season and has been capped on nine occasions by Ireland.
Jennings commented: "It's an exciting time for the province and I am delighted to re-sign with Leinster for a further three years.
"There's a determination within the group to push on and continue to improve and the aspirations of my team-mates as well as the coaching staff was a key factor in my decision to stay.
"Since re-joining the province in the summer of 2008 the province has gone from strength to strength on and off the park and I'm proud to be a part of a set-up that has such strong values and ambitions.
"It has always been my ambition to be a part of a successful Leinster side and I have no doubt that with the competitive nature of the up-and-coming and established members of our squad, the future looks bright."
Meanwhile, Tullow native Sean O'Brien, whose impressive form was recently rewarded with the Bank of Ireland Player of the Month honour for December, is another successful product of the Leinster Academy.
He follows in the footsteps of Cian Healy, a fellow Heineken Cup winner and member of the 2007 Ireland Under-20 Grand Slam winning side, who also recently committed his long term future to the province.
A product of the Leinster Youths system, O'Brien has made 47 Leinster appearances in all, scoring nine tries to date and he has earned four Ireland caps since making his international bow in November 2009.
The 23-year-old O'Brien said: "I am delighted to commit myself for a further three years to Leinster. I believe there is something very special about this side and with so many talented players at our disposal - and the management team is working well - I am keen to be part of a group working hard toward matching the great achievements of recent years and even trying to surpass them.
"While it was flattering to have interest from overseas, I desperately want to be part of the Leinster story for the foreseeable future."
Devin Toner made the first of his three Ireland appearances during the GUINNESS Series in November and since the 2005/06 season, he has made 56 Leinster appearances (including 11 to date in this campaign).
The former Castleknock College lock, who hails from Meath, was a member of the 2008/09 Heineken Cup winning squad and has featured in four Heineken Cup games so far this season.
"I think that the high competition levels within the squad this year have driven us all on and the upshot of that has been our recent good run of form," he said.
"I have been very fortunate to have worked alongside the likes of Mal (O'Kelly), Trev (Hogan), Leo (Cullen) and Hinesy (Nathan Hines) in recent years.
"There's a really strong base within the squad where we're all trying to help each other and improve one another. I'm really pleased to sign up with Leinster."
In 16 appearances so far this season, Fergus McFadden has shown his versatility and consistency in scoring 33 points (including five tries).
The 24-year-old centre, who hails from The Curragh, has won 10 Ireland 'A' caps and was voted the tournament's Most Valuable Player in the 2009 Churchill Cup.
In all, he has played 41 times for Leinster since making his debut in the 2007/08 season.
McFadden said: "I am pleased to commit to my home province because I believe that this is the ideal environment to advance my personal and, most significantly, collective team ambitions.
"It's a really exciting time to be playing here and all of the players and staff share the same determination to push on and become a consistent force both in the Magners League and in the Heineken Cup."
Former Ireland Under-20 prop Jack McGrath has made three senior appearances for Leinster since making his debut last year.
He has also played in seven games in the British & Irish Cup and was a try scorer in the victory over Worcester Warriors on Sunday.
The 21-year-old McGrath added: "I am really enjoying my rugby at present and hopefully I can push on and make it into the senior squad over the coming weeks.
"There's a good incentive for young players to perform well and seeing the likes of Rhys (Ruddock), Dominic (Ryan) and Eoin O'Malley take their chances this year does give you a boost.
"It has been great to learn off the top international talent in the pack and I'm aiming to build on that for the months and years ahead."
Commenting on all five new deals, Leinster head coach Joe Schmidt said: "We are delighted that all five players have committed their long term futures to the province.
"That both Shane and Sean have, at different times, led the team in Leo Cullen's absence this season speaks volumes about the leadership roles that both assume within our panel.
"Both Fergus and Devin have displayed great consistency in their displays this season, while Jack is an exciting front row talent who started off in the Academy and has progressed through to the senior panel.
"All five players have come through the Leinster Academy system and it is vital for the future growth of both Leinster and Irish rugby that we retain our leading indigenous talent.
"It is a timely boost that all five have decided to sign contract extensions at this stage in their careers."