Are there saints that were not Catholic?

Answer 1

There are a number of saints recognized by the Catholic Church who were never Catholics. Most were Jews who died before Christ started his public ministry:
Saint John the Baptist
Saints Elizabeth and Zachary
Saints Anne and Joachim
Saint Joseph
Saint Anna the Prophetess
Saint Simeon the Prophet

Answer 2

In Catholicism, saints are officially recognized by the Church through a formal process known as canonization. However, in other Christian traditions like Eastern Orthodoxy and Anglicanism, individuals who are regarded as saints may not be recognized in the same way by the Catholic Church. Additionally, some non-Christian religions also have figures who are venerated as saints within their respective faith communities.

Answer 3

Of course, the early apostles and Church fathers are universally revered as saints, although they were never formally canonised by the Churches. The formal canonisation of saints is a largely Catholic endeavour, whereas the Orthodox Church tends to venerate as saints those considered worthy, without the formal canonisation process of the Western Church. The Protestant Reformation marked a turning away from the veneration of saints, although the Anglican Church, and to a lesser extent the Lutheran Church, has less formal processes in place for the recognition of saints. Nevertheless, relatively few Protestant saints have been recognised.

Proto-Anglicans such as William Tyndale, Hugh Latimer, Nicholas Ridley and Thomas Cranmer are present in the Anglican calendar of saints, as are Richard Hooker, Lancelot Andrewes, Jeremy Taylor, William Laud, George Herbert, John Donne, edward B. Pusey, John Keble, Bernard Mizecki, and John and Charles Wesley.

The Orthodox Churches recognise Saint Sergius, among others.

The Russian Orthodox Church recognises Saint Seraphim of Sarov.

(Source: A Brief History of Saints, by Lawrence S. Cunningham.)