If you are converting a non EASA ATPL with a valid type rating on a multi-pilot aeroplane, you must meet the minimum experience requirements for an EASA ATPL and pass all 13 theoretical knowledge exams but are exempt attendance of a formal ground school course.

You will need an EASA Class One Medical Certificate (issued by the same state you wish to issue your EASA licence) and also need to pass an ATPL skills test, which is a combination handling check (and IR if appropriate), on the aircraft you are type rated on. This test must be conducted by an EASA TRE on a simulator (or aircraft) approved for the purpose by EASA.

The multi-pilot hours must be flown on an aircraft approved for multi-pilot operations by EASA, and the ATPL Licence Skills Test must be conducted on a multi-pilot type and you must already have that type on your ICAO ATP Licence. If you have been flying a single pilot type but operating it with two pilots, you may still be able to count the hours as multi-pilot if you are able to prove that the company operations manual required a minimum of two pilots.

The Licence Skills Test must still be flown on an EASA multi-pilot type and you must have this type on your ICAO licence. If in doubt, it is vital that you get the agreement of the licence issuing authority that your hours are valid before you commence training.