[2] The PC-21 would be developed and certified as a completely new training system, aimed at meeting future military customers' specifications in terms of capability and life-cycle costs for the next three decades.

In order to achieve this aim, the new trainer was required to have an expanded performance envelope in terms of aerodynamics, cockpit equipment, flexibility, and ease of maintenance.

To meet this goal, the firm chose to incorporate modern materials, an innovative design concept, and full-scale fatigue analysis.

[8] In addition to pilots, various prospective aircrew, such as navigators, weapons officers, and electronic warfare operators, can be trained using the type's embedded simulation/emulation system.

[8] On 30 April 2002, the rollout of the first PC-21 prototype was performed at Pilatus' factory in Stans, Switzerland; this aircraft conducted its first flight on 1 July of the same year.

[11] On 13 January 2005, the second of the two development aircraft crashed in Buochs, Switzerland, while conducting an aerobatic training flight; the accident resulted in the death of the pilot as well as injuring another person on the ground.

The cabin, which is pressurized, is equipped with an On-Board Oxygen Generation System (OBOGS), air conditioning, and Martin-Baker CH16C Zero-Zero ejection seats.

[8] An anti-g system is also present in order to minimize the effects of high g-forces experienced during tactical training and aerobatic maneuvers.

[20][21] In November 2006, the Republic of Singapore Air Force (RSAF) awarded a service contract to Lockheed Martin Simulation, Training and Support (LMSTS) to deliver 19 PC-21 aircraft, to support the RSAF's Basic Wings training course at RAAF Base Pearce in Australia under a public–private partnership (PPP) arrangement, replacing the SIAI-Marchetti S.211.

[29][30] In July 2012, it was announced that the Qatar Air Force had placed an order for a complete pilot training system from Pilatus centering upon the PC-21.

[41][42] In August 2015, Pilatus received a contract to deliver nine PC-9Ms to the Royal Jordanian Air Force, but in April 2016 changed the order to eight PC-21s.

[45] The PC-21 has been evaluated by the Spanish Air Force (along with the Beechcraft T-6 Texan II and the PZL-130 Orlik III), as a possible substitute for its ENAER T-35 Pillan and CASA C-101 Aviojet trainer aircraft.

[46] January 2020 saw the Spanish Air Force confirm an order for 24 PC-21 aircraft, which will replace mainly the CASA C-101 Aviojet, but will also take over advanced training which is currently carried out on the T-35 Pillan.

[47] The Belgian Air Force is also considering the PC-21, among other platforms, to potentially replace its fleet of SF260 Marchetti trainers, which are nearing the end of their service lives.