In 1848, he was the main author of the election law for the Prussian National Assembly, of which he was the president from 27 June to 26 October.
8 elected him in 1849 to the Prussian House of Representatives and he became its president in the first legislative period from February to April.
Due to his oppositional stance over the imposition of the constitution of 5 December 1848, and especially the question of the three class franchise, his election to lord mayor of Magdeburg in 1850 was not confirmed.
Out of protest against the abolition of universal suffrage, against the new electoral law and the re-establishment of the local and provincial assemblies, Grabow withdrew from political life for a while.
In the previous years, he had repeatedly protested against the weak budgetary powers of the second house, which had put him at odds with Otto von Bismarck's ministers.