He was nominated for the position as he was a weak character who posed no real threat to Degrelle's position as leader.
Matthys was also popular with the Germans as he had a long standing admiration for Adolf Hitler.As Rexist leader Matthys proved as weak and ineffective as Degrelle had hoped, although he also demonstrated a propensity towards violence to mask his failings.
His position eventually came under scrutiny after he ordered the massacre of 20 people in Courcelles as a reprisal against resistance activity.
The move was roundly condemned as being too heavy-handed and Matthys gave up the leadership of the Rexists in favour of Louis Collard.
He was sentenced to death for collaborationism and executed.