The two clubs have agreed a fee of £8.2m, according to Goal.
Mignolet has been desperate to leave Anfield in order to play regular first-team football.
The Belgian will return to his homeland after playing 204 times for the Reds following his £9m switch from Sunderland in 2013.
The Reds will now look to sign a back-up goalkeeper for Brazilian star Alisson.
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