No, to fly as a pilot-in-command on Cessna C525 Citation you do not need to have an airline transport pilot license ATPL(A).

The reason is that the fact that the Cessna C525 Citation aircraft is from a certification point of view a single-pilot aircraft high performance complex aeroplane operated in multi-pilot operations. The EASA Type Ratings and License endorsement list, the Cessna C525 Citation recognises as a single-pilot aircraft.