Ian Peel will serve as scrum coach for England's RBS 6 Nations campaign while also joining Saracens' backroom staff on a permanent basis.
The former Newcastle Falcons prop has coached England's Under-20s since 2013, but will now relinquish that role.
The 39-year-old will assist Eddie Jones in his first Six Nations, the Rugby Football Union has announced, though the new England boss could then seek a full-time scrum specialist appointment.
Peel's appointment at Saracens offsets the Aviva Premiership club's impending loss of Paul Gustard, who will join Jones' England set-up in the new year.
"This is a huge opportunity and I am really looking forward to getting stuck in with lots of the guys who I have worked with through the age-group teams but also when I have gone in and helped Graham Rowntree over the last few seasons," said Peel, of working with England for the Six Nations.
"It is a huge honour to go and deliver that for the seniors and joining up with Eddie, Steve Borthwick, Paul Gustard and the rest of the team."
Former Newcastle scrum coach Peel has been part of a hugely-successful Under-20s set-up for England, integral to Junior World Championship triumphs in 2013 and 2014.
Peel headed up the coaching team that took England to the finals again this year, and that age-group success has not gone unnoticed.
New head coach Jones was thought to have weighed up adding his former Japan colleague and Brave Blossoms scrum guru Marc dal Maso to the England ranks.
Dal Maso is keen to keep coaching at the highest levels despite recently revealing he suffers from Parkinson's disease.
Whether or not England turn to Dal Maso, Peel's appointment allows Jones and the RFU breathing room over selecting a long-term specialist scrum coach.
"I have been coaching within the RFU pathway for the last six years so this is a huge chance to go and coach seniors players at a quality club that performs at the highest level domestically and in Europe," said Peel of his new role at Saracens.
"I have no doubt it will be a great environment to work in and there are a number of players who I have worked with within the England age-group set-up like Maro Itoje, George Kruis and Mako Vunipola.
"I am really looking forward to getting involved in the day-to-day and the hands-on coaching every week.
"I have loved every minute of working at the RFU, not just with the Under-20s but all the age-group sides within the pathway.
"It has massively developed me as a coach by working with different teams and different players and learning from those players and coaches.
"To develop as a coach under the likes of Kevin Bowring and Richard Shuttleworth has been great.
"Every team I have worked with has been different but I have massively enjoyed my time with all of them and for different reasons.
"Not just the success that went with the Under-20s with the Junior World Championships but seeing players that have developed through the pathway then go on and play in the Premiership or Championship and then ultimately going on and represent England or the British and Irish Lions. That is the biggest honour."
Jon Callard will lead England Under-20s' Six Nations programme, assisted by forwards coach Peter Walton.
Former Gloucester fly-half Rory Teague will look after the Under-20s backs, after moving to the RFU from a coaching role at Saracens' academy.
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