The 39-year-old had combined the age-grade role with his job at Melrose but is re-uniting with his old Under-20 boss Sean Lineen at the Exiles club, who have a partnership agreement with the SRU, as forwards coach.
The former Melrose, Gala and Borders forward, who also played a season for London Scottish in the 1990s, has developed a reputation as one of the country’s most promising young coaches having won three Premiership titles and a Scottish Cup with the Greenyards club and achieving notable victories over England and Australia as Scotland Under-20s chief.
He now gets the chance to go fully professional at the Athletic Ground in Richmond, where the link-up with BT Murrayfield which was announced in January has been resurrected following a temporary halt in the spring. Last week five Scotland Under-20 players were loaned to London Scottish, with hooker Cameron Fenton accompanying back-row Ally Miller, scrum-half Hugh Fraser, centre Tom Galbraith and wing Ben Robbins.
The partnership has been scaled back after it was initially proposed that up to 14 young players could be made available to the London club. A dramatic and acrimonious breakdown in relations between the club and the union was subsequently patched up and selected pro-team, BT Sport Scottish Rugby Academy and Scottish age-grade players will be based at Richmond and be available to London Scottish for Championship and British &Irish Cup fixtures.
Dalziel said: “I have been presented with a fantastic opportunity for me to challenge myself at this stage in my life and my coaching career.
“It’s the start of a new chapter and I look forward to joining such an ambitious club at this exciting time.”
The Borderer had served as Lineen’s assistant with the under-20s until the 1990 Grand Slam hero moved on to become London Scottish director of rugby at the start of the year. Dalziel went on to lead the young Scots to a historic first-ever win over their English counterparts and another success over Italy in the junior Six Nations. He then led them to a joint best-ever finish of eighth at the Under-20 World Cup in Manchester, where they defeated Australia 15-10 in their opening match.
Dalziel will work with London Scottish head coach Peter Richards and replaces former Edinburgh flanker Roddy Grant, who had a stint as forwards coach under Lineen last season.
Lineen said: “John [Dalziel] has enjoyed a lot of success in Scotland’s BT Premiership, and has been in the international under-20 programme for a number of years, so this appointment is another important step in his coaching career.
“Scottish Rugby’s partnership with London Scottish is helping us further develop our pathway for aspiring young coaches, as well as aspiring young players, that need game time at a certain level to help them progress into the professional environment.
“It’s a big commitment, an excellent opportunity and I’m delighted he’s taking it on.”
The SRU will now look to appoint a new Scotland Under-20 chief, while backs coach Rob Chrystie has been confirmed as the new Greenyards boss.
The former Hawick, Melrose, Bath and Scotland A scrum-half said: “I am deeply honoured to be taking on the role of head coach at Melrose.
“It has been a great experience working with John [as his assistant] and learning from him.
“It is a new beginning and we have a very exciting young squad for the coming season and I can’t wait for it to start.”
Melrose president Trevor Jackson added: “Over the past 11 years as a player, forwards coach and head coach, John has contributed to helping Melrose stay at the forefront of Scottish club rugby.
“He is a big character who brings an edge, skill and insatiable energy to everything that he does. We wish him all the best for the future in his much-deserved full-time role with Scottish Rugby.”