In 1612 he took his Master's Degree in Copenhagen and, in the same year, became a parish pastor in Køge, Denmark.
The next year, he was engaged to marry Karen Andersdatter but she left him for King Christian IV.
Here he performed his duties well, was eager for education of the youth and for moral order, and made himself so popular in his diocese, that, unlike his predecessor "The Evil Bishop" Niels Claussøn Senning, he was called “den gode Bisp [The Good Bishop]”.
In 1636 he consecrated a gymnasium [high school] in Christiania, and sought to obtain talented teachers for it.
When Glostrup became ill in 1638, Boesen assisted him in the execution of the official duties and, in the following year, succeeded him as the eighth Lutheran Bishop of Oslo, when Glostrup died.