Inglethorpe replaces Rodolfo Borrell as U21 Liverpool coach, with the Spaniard being named as head of academy coaching.
Frank McParland continues with his role as Academy director, with first-team manager Brendan Rodgers praising his contribution to the club's continued commitment to developing exciting young talent.
Rodgers commented to liverpoolfc.com: "I'm delighted that Alex has decided to join us in our journey to create a philosophy that runs directly through the club. He has many years of experience in youth football and also managed at senior level. His unswerving belief and commitment to our way of working will bring continued success in this role.
"I've been extremely impressed with Rodolfo in my short period at the club. His thinking is very similar to mine in the best way to educate and develop players. His role will make richer the philosophy we are creating at the club from U9s through to the first team.
"I'm also delighted with the great work done by Frank McParland in leading the Academy and I look forward to working closely with him to continually develop our talents to play for the first team."