Bruno was from a noble family of Querfurt, Saxony. He is said to have been a relative of the Holy Roman Emperor Otto III. At the age of six he was sent to be educated in Magdeburg, seat of Saint Adalbert. While still a youth he was made a canon of Magdeburg cathedral.
The fifteen-year-old Otto III made Bruno a part of his royal court. While in Rome for Otto's imperial coronation, Bruno met Adalbert of Prague, who was martyred a year later. Bruno spent much time at the monastery where Adalbert had become a monk and where abbot John Canaparius wrote a life of Saint Adalbert . Bruno entered a monastery near Ravenna, founded by Otto, and underwent severe ascetic training under the guidance of St. Romuald.
The pope appointed Bruno to mission among the pagan peoples of eastern Europe. Because of conflict between the Empire and Boleslaus I, duke of Poland, Bruno set out from Mainz for Hungary. There he went to the places that Saint Adalbert of Prague had attended. Bruno tried to convert the leader of "Black Hungary" named Achtum or Axum, but he encountered strong opposition, including that of the Greek monks there.
After this failure, Bruno went to Kiev, where Grand Duke Vladimir I authorised him to make converts among the Pechenegs north of the Black Sea between the Danube and the Don rivers. The Pechenegs were considered the fiercest of all the pagan peoples, but Bruno spent five months there and baptized many. He helped to bring about a peace treaty between them and the Kiev ruler. After consecrating a bishop of the area he went to Poland.
In Poland he consecrated a bishop from Sweden. While there he found out that his friend Benedict and four companions had been killed by robbers in 1003. Bruno took eyewitness accounts and wrote down a touching history of the so-called Five Martyred Brothers. In 1008 Bruno wrote a letter to Henry I, Holy Roman Emperor. exhorting him to show clemency towards Boleslaus I.
At the end of 1008 Bruno and eighteen companions set out to found a mission among the Prussians, but met with little success. They then traveled to the north-east, preaching everywhere they went. In 1009 at the Baltic Sea coast near Braunsberg they were martyred. Annals of the monastery of Quedlinburg wrote about it. It was the first time Lithuania was mentioned. Duke Boleslaus bought the bodies and had them brought to Poland. Soon after Bruno and his companions were revered as martyrs and Saint Bruno was canonized.
The city of Braunsberg (earlier Brunsberg) in east Prussia was named for Saint Bruno.