In 1949 Marijnen became secretary of the Agricultural Society and in 1951 Secretary-General of the Foreign Agricultural Trade Department of the Ministry of Agriculture, Nature and Food Quality.
Pada 1949 Marijnen menjadi sekretaris Kelompok Pertanian dan pada 1951 Sekretaris Jenderal Departemen Perdagangan Pertanian Luar Negeri di Kementerian Pertanian, Perikanan, dan Pangan.