A young man and a crafter, Gregersen came to Budapest, Habsburg Empire in the 1850s, where he established a company within general contracting. After a few years, the company had become one of the leading in the Kingdom.
Living in the town Szob, near to Budapest, Gregersen was married with Aloyzia (Luise) Sümegh (1836–1906), a daughter of Josef Sümegh and Katharina Stitz. They had 19 children together, of whom seven died as infants.
Gregersen designed the Elisabeth Bridge between the two parts of the city of Komárom, Austria-Hungary (today between the cities of Komárom, Hungary and Komárno, Slovakia. He also designed and lead the carpenter works on the building of the Hungarian Parliament and the Museum of Fine Arts and on the former building of the National Theatre in Budapest.
In 1884 Gregersen with wife and (some) children were ennobled by Francis Joseph, Apostolic King of Hungary. They were also granted a coat of arms which, in the upper field, displays the Norwegian Lion.