Longwell, a former colleague of Caldwell's at St Mirren, has joined Shrewsbury after leaving former club New York Red Bulls in November.
The Scot replaces former academy boss Eric Ramsay, who was promoted to Sam Ricketts' first-team coaching staff following a successful period in interim charge.
Longwell was head-hunted by the Red Bulls after originally leaving Scotland to join Orlando City.
Caldwell said: “It’s a coup to get him here to Shrewsbury, we think he’ll be a great asset to this football club.
"The academy has progressed quite considerably over the last few years and for me David is one who can continue that progression.
"I sold it to David about the potential that we’ve got, I think there’s always more that we can do to improve things.
"He’s got a fantastic reputation in Scottish football, and now in America, so for me it’s a great addition."
Longwell, who has UEFA Pro Licence,Youth Directors Award and Youth Licence badges, helped progress a number of St Mirren youngsters to the top clubs in Scotland, as well as current internationals.
He said: "I'm really happy to be here.
"I'm really impressed with what they've done here. There's a really good foundation and base, the challenge for me is to take it on to other levels."