Lawrence will start work on September 1 following his summer departure from Manchester United, where he did an excellent job in charge of the Under-18s.
Lawrence led Manchester United's youngsters to three pieces of silverware in the 2023/24 season, winning the Premier League regional and national titles as well as the Premier League Cup.
Last term, his side finished second in Premier League North and reached the semi-finals of the FA Youth Cup, eventually suffering penalty heartbreak at the hands of Aston Villa.
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As well as leading the Under-18s side, Lawrence was Manchester United's head of player development for Under-13s to Under-16s.
The 38-year-old previously spent eight years at Charlton Athletic's academy, where he worked his way up to become the club's head of coaching.
Lawrence will replace Diarmuid O'Carroll., who left Newcastle to become first team coach at Sparta Prague earlier this summer. He will be assisted by former Middlesbrough defender Robbie Stockdale, who has been in interim charge since O'Carroll's exit.
"It's a real privilege to join Newcastle United and to lead the Under-21s squad at such an exciting time for the academy," said Lawrence.
"I've always believed in creating environments where young players can grow - not just as footballers, but as people - and that is something the academy does very well.
"The club has a clear vision for development, and I'm looking forward to working with the staff and players to help each individual take the next step in their journey."
Harper, Newcastle's academy director, said: "We are delighted to welcome Adam to Newcastle United as new Under-21s Lead Coach.
"We have carried out a thorough recruitment process to ensure we find the right person to nurture and develop our young players, and in Adam, we have an outstanding young coach joining the club.
"His record speaks for itself but results only tell part of the story. Throughout his career, he has prioritised the individual development of the young players he has worked with, and he will play a key role in supporting our talent pathway into the first team.
"I'd also like to thank Robbie Stockdale and everyone connected with the Under-21s for their hard work and collaborative approach while we recruited into this position."