Jan Martyniak was born in Spas near Staryi Sambir Raion from Vasyl and Maria Zygmunts, a farming family.

Years were spent in a Spas, where the religious life of the inhabitants of dominant influence was the famous monastery of St. Onofriy Basilian Fathers in nearby Ławrowie.

The father of the future Metropolitan was drafted during World War II by the Soviet Army and was killed in a German POW camp near Dresden.

Wishing to devote himself to the clerical state, Martyniak studied theology at the Seminary in Wroclaw and graduated in 1964, receiving his priestly ordination by Archbishop Boleslaw Kominek's hands.

On 22 December 1981 Polish Primate Jozef Glemp gave him the job of vicar general of the faithful of the Byzantine-Ukrainian rite for the Southern Vicariate.

In 2009, the World Union Army of the Volhynia District asked the Archbishops Stanislaw Dziwisz, Kazimierz Nycz and Jozef Michalik to support the protest against the behavior of John Martyniak and the Greek Catholic Bishop Włodzimierz Juszczak, accusing them of slander persons as Father Tadeusz Isakowicz-Zaleski, falsification of history and the development of proper ground for the rebirth of Ukrainian nationalism.