The move is a sign that Francis is looking to improve the Holy See's response to abuse at a time the church and papacy are facing a credibility crisis.
Francis named Archbishop Charles Scicluna as a deputy, or adjunct secretary, at the Congregation for the Doctrine of the Faith, the Vatican office that processes sex abuse cases.
Archbishop Scicluna had been the congregation's chief prosecutor for a decade and was credited with turning the church around, with new procedures making it easier to defrock paedophiles.
However, Pope Benedict XVI sent him to his native Malta in 2012 as bishop after his tough line ruffled too many feathers in the Vatican bureaucracy.
Archbishop Scicluna retains his Malta post.
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