Hesemann studied History and Cultural Anthropology at the University of Göttingen in Germany. He lives in Düsseldorf and Rome, where he is accredited to the Holy See Press Office. He is also one of the few academic historians who were granted access to and did research in the Vatican Secret Archives.
His 28 books were published in 14 languages (German, English, Spanish, Italian, Czech, Slovak, Hungarian, Romanian, Croatian, Greek, Polish, Russian, Dutch, French) with a world print-run of nearly two million copies. Hesemann lectured on international conferences and at over 30 universities of all five continents, including the Vatican Lateran University.
With official permission from the Vatican, he investigated the history of the alleged relic of the inscription of the cross of Jesus, hidden in Rome for nearly 1700 years. It was dated by seven Israeli experts for comparative palaeography —the established method to date inscriptions- into the 1st century, indicating its authenticity.
On December 17, 1998, Hesemann was personally received by H.H. Pope John Paul II to present the results of his study on this important relic. Later, in a letter written by his personal secretary, John Paul II expressed Hesemann his “admiration and appreciation for your laborious research”. Hesemann's conclusions were later confirmed by the work of Prof. Maria-Luisa Rigato of the Pontificial University Gregoriana in Rome and Prof. Carsten Peter Thiede of the Universities of Basle (Switzerland) and Beer-Sheva (Israel). His subsequent book “Titulus Crucis” (The Jesus-Title) became a bestseller in Germany and Italy, published by the leading Catholic publishing houses of both countries, Herder (1999) and San Paolo (2000). The relic, exhibited in the Basilica di Santa Croce, became one of the major pilgrim's attractions during the Holy Year 2000.
Hesemann delivered the German language reading in the Easter Night Vigil 1999, the last of the 20th century, presided by the Pope, in St. Peter's Basilica in Rome. He was personally invited to participate in the opening and closing of the “Holy Year 2000” and travelled with Pope John Paul II to Poland, the Holy Land and Fátima, Portugal. He followed the publication of the Third Secret of Fatima and personally interviewed several high ranking Curia members including Archbishop Tarcisio Bertone, Secretary General of the Congregation for the Doctrine of Faith (today Cardinal Bertone, the Vatican’s Secretary of State), one of the Vatican’s major departments.
In the “Holy Year” 2000, Hesemann released his book “The Silent Witnesses of Golgota” in German, followed by an Italian translation (Edizioni San Paolo) two years later. It is the first complete study on the relics of the Passion of Christ. Hesemann was invited to present it personally to His Holiness, Pope John Paul II., during an audience on June 6, 2001. Archbishop Stanislaus Dziwisz, the Personal secretary of the Pope, commented beforehand: “Your unique book has moved me to tears. Receive my deepest thanks and my appreciation for your sacrificial research work on the most holy relics of the Church of God! Praying I contemplate in this Holy Week on the silent witnesses of Golgota you worked on.” .
In 2003, two more books on Christian relics followed, “The Discovery of the Holy Grail” and “The First Pope”, which describes the fascinating story of the discovery of the tomb of St. Peter beneath St. Peter's Cathedral in Rome. Again, Hesemann was invited to present the book personally to the Holy Father, this time on the eve of his 25th Jubilee, October 15, 2003. “Joy, gratitude and appreciation are my feelings for you to salute your book ‘The First Pope’ adequately Finally we have a profound scientific study on Peter, Prince of the Apostles”, Archbishop Dziwisz wrote on October 28, 2003. The book was written in close cooperation with Bishop Vittorio Lanzani of the Fabbrica di S. Pietro and the renowned Church historian Prof. Dr. Eva-Maria Jung-Inglessis, Rome, and includes many never-before-published photos of the Vatican excavations.
In March 2006, on request of the Cofradia of the "Caballeros del Santo Caliz", Hesemann briefed Pope Benedikt XVI and Archbishop Piero Marini, Master of Liturgical Ceremonies of the Holy Father, on the "Santo Caliz" (Holy Chalice) in preparation of the Holy Father's announced trip to the World Family Meeting in Valencia. Indeed on July 8, 2006 Benedict XVI "halted before the celebrated relic of the Holy Chalice", as he told the Valencians later. The next day, July 9, he celebrated Mass with it in front of over 2 Million people.Hesemann also contributed to the first interdisciplinary publication on the Holy Chalice, released by the Valencian Library in colloboration with the Archdiocesis Valencia in May 2006. Furthermore he was invited to speak at the First International Congress on the Holy Grail, organized by the Archdiocesis Valencia in November 2008.. In 2003, in appreciation of his work, Hesemann was invited to become a “Caballero del Santo Caliz” (Knight of the Holy Grail) himself, a member of the noble Confraternity under the auspices of the Cardinal Archbishop of Valencia, Don Agustin Garcia-Gasco.
He followed Pope Benedict XVI on his trips to Germany (2005, 2006), Spain (2006) and Israel (2009). On June 6, 2007, he was received by the Pope in an audience and presented him his latest book on the "Black Legends" of the Church history. In October 2007, he commented the publication of documents on the Knight Templars by the Vatican Secret Archives for "Die Welt", Germany's most respected national daily newspaper.
In April 2008, after research in Greece, Cyprus, Turkey, Israel and Malta, Hesemann published "Paulus von Tarsus", an "archaeological biography" of St. Paul, on occasion of the "Pauline Year 2008/9", inaugurated by Pope Benedict XVI on June 28, 2008. His book features the first forensic reconstruction of the face of St. Paul, done by experts of the State Bureau of Investigations (Landeskriminalamt) of Northrhine-Westphalia. Hesemann runs the German language website on the Pauline Year,. He also worked as a lecturer on St. Paul for the Educational Department of the Archdiocesis of Cologne and was invited by the Diocesis of Regensburg — the home diocesis of the Pope — to educate their deacons on Church history. In recognition of his work, he was received by the Pope in a second audience on June 25, 2008 and was invited to participate in the opening ceremony of the Pauline Year in the Papal Basilica St. Paul Outside the Walls.
In October 2008, he published his latest book, "The Pope who Defied Hitler. The Truth about Pius XII" for which he did research in the Vatican Secret Archives and consulted with the Relator and Postulator of the ongoing Beatification Process of this great wartime Pope who saved the lives of over 850.000 Jews during the Holocaust. When Pope Benedict XVI received Hesemann in a third audience on October 8, 2008, he thanked the author for "your good and important work". His latest discoveries, proving that Pacelli was not only far away from being “Hitler’s Pope” but indeed an early supporter of Zionism, made international headlines in early 2009. Since November 2008, Hesemann advises and represents the “Pave the Way Foundation” with the aim to remove obstacles between the world religions and especially to improve the relationship between Judaism and Catholicism . His future projects include an “archaeological biography” of Jesus Christ, a picture documentation on the life of Pope John Paul II, for which he works exclusively with the retired Papal photographer Arturo Mari, and a major exhibition on Christian relics and reliquaries in Hong Kong.