Calm, who spent the last three years coaching at Blues sister club UE Cornella, will lead the Under-23s Development Squad.
The 37-year-old Spaniard will be assisted by Steve Spooner, who has moved from his role as Blues Under-18s Coach to Senior Professional Development Coach.
Calm spent two years as an assistant at Cornella before stepping into the Head Coach role and leading them to the Segunda División B Play-Offs last season.
They also qualified for the Play-Offs when he was assistant.
Calm has significant experience in Segunda B working with senior and development players.
Kristjaan Speakman, Blues Academy Manager, commented: "Xavi arrives having been involved in a period of success at UE Cornella where the team progressed to the Play-Offs for two consecutive seasons in Segunda B.
"Importantly, he’s also been instrumental in the transition of several players from their Under-19s team to their senior group and these experiences combined are going to be important for our players.”
At the end of June the Club announced that Paul Robinson had become Lead Professional Development Coach - guiding the Under-18s - and Andy Crabtree Academy Development Coach. Spooner switched from the Under-18s to the Under-23s.