Are non-Catholic baptisms valid?

[Gerardello]

Have Catholic Church ever re-baptized the converts from orthodox church? How orthodox baptism can be valid if they deny supremacy of Holy Father, proceeding of Holy Spirit from Son, Purgatory and some other important dogmas?

 

[Fr.Charles_Grondin]

All that is required for baptism is the proper matter (water), the proper form (Trinitarian forumla) and that the minister of the sacrament intend what the Church intends. Any Christian who views baptism as instituted by Christ to forgive original sin and actual sins has the proper intention to validly baptize. The Orthodox Church shares in this understanding of baptism (even if there are slight nuances). However pretty much anybody can validly baptize as long as they have the right intention:

Pope Eugene IV’s Papal Bull Exultate Deo:

The minister of this sacrament is the priest, to whom it belongs to baptize, by reason of his office. In case of necessity, however, not only a priest or deacon, but even a layman or woman, nay,** even a pagan or heretic can baptize**, provided he observes the form used by the Church, and intends to perform what the Church performs.