Mouallem was born in Eilabun, Galilee, in 1928 and received his education at the Minor and Major Seminaries of St. Paul Missionaries, Harissa, Lebanon, and was ordained a priest in 1955.
He finally returned to Lebanon to teach theology, liturgy and Islamology at St. Paul's High Institute, Harissa.
He was consecrated bishop of Melkite Greek Catholic Eparchy of Nossa Senhora do Paraíso em São Paulo, Brazil, on 29 June 1990.
[3] The Holy See noted that selection of a bishop was matter reserved for the Church, "free of all external pressure", and that the Fundamental Accord between the Holy See and the State of Israel "provides for the autonomy of Church and State, each one in its own area.
Later, in October 2002, Archbishop Mouallem was prevented by Israeli airport guards from leaving Jerusalem to attend an interfaith meeting in London.