V rokoch 1980-1985 študoval teológiu na CMBF v Bratislave. Za kňaza bol vysvätený 16. júna 1985 v Nitre. V pastorácii ako kaplán pôsobil v Nitre a v Drietome, kde bol aj správcom farnosti do r. 1990. V tomto čase postgraduálne študoval na CMBF v Bratislave, kde získal r. 1991 doktorát posvätnej teológie. Dňa 1. septembra 1990 bol menovaný za prefekta Kňazského seminára sv. Gorazda v Nitre a 18. októbra 1991 za cirkevného sudcu. Od r. 1990 prednáša cirkevné dejiny na RKCMBF UK v Bratislave a na Teologickom inštitúte v Nitre. V r. 1991-2005 tiež pôsobil aj na Vysokej škole pedagogickej v Nitre, na katedre etiky a katechetiky (dnes Univerzita Konštantína Filozofa). Dňa 1. júla 1993 bol menovaný za docenta Cyrilometodskej bohosloveckej fakulty UK v Bratislave. V r. 1995-1998 bol prodekanom spomínanej fakulty. V čase od 1. júla 1996 do 1. júla 2001 zastával funkciu rektora Kňazského seminára sv. Gorazda v Nitre. Svätý Otec Ján Pavol II. ho v roku 1997 menoval za „kaplána Jeho Svätosti“ (Mons.). Vedúcim Katedry cirkevných dejín CMBF UK v Bratislave bol v r. 1997-2006. Dňa 13. decembra 1997 ho prezident Slovenskej republiky menoval za profesora v odbore „katolícka teológia“. V r. 2001 bol Akademickým senátom zvolený za dekana Rímskokatolíckej cyrilometodskej bohosloveckej fakulty Univerzity Komenského v Bratislave. Funkciu zastával do r. 2004. Dňa 9. júna 2005 bol menovaný za nitrianskeho biskupa pápežom Benediktom XVI. a konsekrovaný na biskupa bol v Nitre 16. júla 2005. Od októbra 2006 do septembra 2015 bol podpredsedom Konferencie biskupov Slovenska (KBS). Stojí na čele Komisie pre klérus a Rady pre históriu KBS. Ako historik zaoberá sa obdobím kresťanského staroveku a stredoveku so zreteľom na slovenské cirkevné dejiny. Je autorom viacerých monografií z oblasti cirkevných dejín a duchovnej literatúry.

In the years 1980-1985, he had been studying theology at CMBF in Bratislava. He was ordained a priest on the 16th of July, 1985 in Nitra. He has been serving as a chaplain in Nitra and Drietoma, where he has also been a parish administrator until 1990. At this time he had been studying in CMBF in Bratislava, where he had got his Ph.D. in sacra theologian. On the 1st of September, 1990 he was appointed a prefect of the Clerical Seminary of St. Gorazd in Nitra and on the 18th of October, 1991, an ecclesiastical judge. Since 1990 he has been teaching Church history at RKCMBF UK in Bratislava and the Theological Institute in Nitra. In 1991-2005 he had been teaching also at the Pedagogic University in Nitra, at the department of ethics and catechetics (today Konštantín Filozof University). On the 1st of July, 1993 he was awarded the title of docent of the Cyril and Methodius Theological Faculty UK in Bratislava. In 1995-1998 he was a vice-dean of this faculty. From the 1st of July, 1996 to the 1st of July, 2001 he has been a rector of the Clerical Seminary of St. Gorazd in Nitra. In 1997 the Holy Father John Paul II appointed him „the Chaplain of His Holiness“ (Mons.). He has been a head of the Department of Church History in 1997-2006. On the 13th of December, 1997, the President of the Slovak Republic had appointed him Professor in the field of „catholic theology“. In 2001 he was elected Dean of the Roman Catholic Cyril and Methodius Theological Faculty of the Comenius University in Bratislava. He had performed this function until 2004. On the 9th of Juni, 2005, he was appointed the Bishop of Nitra by Pope Benedict XVI, and he was consecrated Bishop in Nitra on the 16th of July, 2005. From October 2006 to September 2015, he had been a vice-president of the Episcopal Conference of Slovakia (KBS). He is the head of the Committee for Clergy and the Council for History of KBS. As a historian, he has been searching the Christian Antiquity and Middle Ages concerning Slovak Church history. He is an author of several monographs in the field of Church history and spiritual literature.