He transferred to the Vilnius Priest Seminary in 1824, from which he graduated in 1828.
Early in his youth, he had his baptismal records altered to indicate noble birth. The family name was Polonized to Wołonczewski. This practice, not uncommon among prosperous villagers, was a means of providing educational opportunities otherwise denied to peasant children.
In 1816 he entered the Dominican school at Žemaičių Kalvarija and six years later began his studies at the Theological Seminary in Varniai.
Ordained a priest that same year, he spent the next six years teaching religion in Belarus. In 1834 he returned to Lithuania to take up a teaching position at the Kražiai College.
In 1840 he was assigned to the Vilnius Theological Seminary, where he lectured in pastoral theology and biblical archaeology and where he earned his doctorate in theology in 1842. That same year on orders of the Tsar, the Academy, its teaching staff and student body, was moved to Saint St. Petersburg, Russia.
Valančius came back to Lithuania because of health problems in 1845 and was appointed rector of the Varniai Theological Seminary, serving in this capacity until 1850.
Having been absent from Lithuania during the anti-Russian uprising in 1831, Valančius was considered to be relatively apolitical, and thus the Russian government did not object when he was proposed as Episcopal candidate for the see of Samogitia. He was consecrated bishop in 1850, the first peasant to head over that diocese. Taking up his duties, he guided the diocese for the next 25 years, years of religious, political and social change not only within Samogitia but in Lithuania as a whole.
He expanded and improved the Samogitian parochial school network, wrote a many religious books, and in 1858 inaugurated a temperance movement, which grew to encompass nearly a million members, almost half of the county’s population. he also wrote first Lithuanian language history of Samogitian diocese, that has not lost its scientific value until nowadays.
His pastoral and educational work was interrupted by the uprising of 1863–1864 and was made extremely difficult as the Russian government tightened its reins after the collapse of the revolt. Yet these circumstances did not prevent him from following a course which could not but bring him into direct conflict with the authorities.
He made every effort to undermine the government’s scheme of Russification. In 1874 Valančius fell ill and died in Kaunas on May 29, 1875.
He was interred in the crypt of the Kaunas Cathedral Basilica.
His services to the Lithuanian cause were lasting and important. His opposition to the Russian government and the tactics he employed in resisting its policies, particularly Lithuanian press ban. He sponsored the illegal practice of printing Lithuanian books in East Prussia and smuggling them into Lithuania by knygnešiai, served to stimulate the emergence of the Lithuanian national movement.
An educator, and able Church administrator, historian and ethnographer, and a talented writer, Valančius emerges as one of the most versatile and influential figures in the 19th century Lithuania.