Crawley, who nurtured the talents of some of Australia's best glovemen including Danny Vukovic and Mat Ryan, parted ways with the Mariners after a decade with the club and eight years in the coaching post.
The 43-year-old worked with Arnold for three years in Gosford from 2010 to 2013, during which time the pair helped guide the side to two A-League grand finals and one premiership with a focus on developing young players.
He'll replace Zeljko Kalac, who was granted a release from the final year of his contract to join cross-town rival Western Sydney Wanderers, and will get busy working with shot-stoppers Vedran Janjetovic and Anthony Bouzanis.
"I am delighted to be joining Sydney FC and to be working with Arnie once again," Crawley said.
"The club had an excellent season under his guidance last year and I'm very excited to see what we can go on to achieve both in the A-League and in Asia this year."
Crawley's work with Australia keeper Ryan earned plaudits, as did his role in developing his predecessor Vukovic into a sought-after star.
Arnold said his former colleague's pedigree spoke for itself.
"John Crawley is one of the best, if not the best goalkeeper coach in the country," he said.
"I am looking forward to seeing how Vedran and Anthony develop under his tuition and for them to be open-minded to experiencing new goalkeeping methods."