He was interested in the judicial philosophy of Friedrich Julius Stahl and the economic theories of Karl Ludwig von Haller regarding political legitimacy.
He followed the usual legal career, becoming a law clerk in 1838 at the Higher Regional Court of Frankfurt (Oder) under vice president Ludwig von Gerlach and worked from 1844 to 1847 as an attorney at the Prussian land-improvement bureau and later at the consistory at the province of Saxony.
In 1847 he became an appellate court attorney representing the consistory in Madeburg where he was assigned to prosecute liberal clergyman Leberecht Uhlich.
Through his close-working with Otto von Bismarck, Wagenar became one of the best-known and controversial conservative pundits.
In 1854 he retired from editing the newspaper (called the Kreuzzeitung because it featured a large iron cross) and invested his severance in a scheme in Neustettin (now Szczecinek) and worked as a criminal lawyer in Berlin.
He became a clever and quick-witted speaker of the Prussian House of Representatives (Preußisches Abgeordnetenhaus) and provided great service to his party from 1867 in the North-German and from 1871 in the German Reichstag.