Penrith-born Lancaster has been kept on in the role of senior coach by the Guinness Pro12 outfit with head coach Leo Cullen being handed a two-year contract extension.
Assistant coaches Girvan Dempsey and John Fogarty have been retained by Leinster, too.
Lancaster, from Culgaith, near Penrith, joined Cullen’s coaching staff last year after leaving his post as England coach in November 2015.
“Stuart has had a huge impact on this club since his arrival in early September and he brings with him a wealth of experience both on and off the field that has helped Leo and the other coaches and players massively,” Leinster CEO Mick Dawson said.
“His dedication to the Leinster cause is there for all to see and he has been welcomed with open arms by everyone at the club.”
Head coach Cullen, who won 221 caps for Leinster and was captain of three Heineken Cup-winning squads, was appointed at the start of the 2015/16 season and will lead his coaching team for a further two seasons until the end of their 2018/19 campaign.
On Cullen’s work with the club, Dawson added: “I think Leo deserves enormous credit for the way he has stepped up to the mark over the last two seasons.
“There have, of course, been challenges and disappointments but already in his short career as head coach, he has led Leinster to a Guinness Pro12 Final and to successive top two regular season finishes.
“He has led the club to the last four of the Champions Cup this season, having already finished top of the pool and they went very close to reaching a first Champions Cup Final since 2012.
“We are delighted to have secured his services for another two seasons.”
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