Arūnas Poniškaitis was born on August 1st, 1966 in a devoutly practicing Catholic family. He was christened in the Griškabūdžio church and lived in his native village of Vyšpiniai (in Šakiai) in the parish of Žvirgždaičiai up until the age of four. Then his family lived in Vilkaviškis, where he finished the Second Middle School in 1984 (the current Aušros High School). After required service in the Soviet army, he was accepted into the Kaunas Priest’s Seminary in 1987. He completed his studies on May 31st, 1992 and received his blessings from Bishop Juozas Žemaitis MIC and was assigned as vicar at the Church of Guardian Angels in Alytus. He continued his theological studies at the Pontifical St. Grigalius University in Rome, where he received a degree in Theology in 1997.
In 2001, he received a PhD in Theology. Upon his return to Lithuania, he was appointed as parish pastor at St. Casimir’s parish in Alytus. From 2001–2004, he was the Spiritual Father at the Blessed Jurgis Matulaitis Seminary in Marijampolė, part of the Vilkaviškis Diocese. From 2001–2009 he taught fundamental theology at Vytauto Didžiojo University, courses at the Seminary in Marijampolė, and the College in Marijampolė. In 2003, Fr. Arūnas Poniškaitis was appointed as the Notary for the Curia of the Archdiocese of Vilkaviškis. In 2004, he was appointed as the bishop’s General Vicar in Vilkaviškis. In 2005, he was given the title of chaplain-monsignor by the Holy Father. He was also a member and consultant of the Vilkaviškis Diocese Priest’s Council and the chaplain for the Faith and Light Community in Marijampolė. He acted as a Vilkaviškis Diocese representative for the publication Bažnyčios Žinios, and is also the spiritual advisor for the Ateitininkų Federation’s board members in Marijampolė.
On February 5th, 2010, Pope Benedict XVI appointed Monsignor Arūnas Poniškaitis to the Vilnius Archdiocese as a Bishop Auxiliary and a Titular Bishop of Sinna.
On March 4th, 2010 he was consecrated Bishop in the Archcathedral. On the same day, Cardinal Audrys Juozas Bačkis appointed him as General Vicar. Archbishop Metropolitan Gintaras Grušas renewed this position in 2013.