Hendra and Nipah viruses (genus Henipavirus family Paramyxoviridae) are highly pathogenic bat-borne viruses. The need for high biocontainment when studying henipaviruses has hindered the development of therapeutics and knowledge of the viral infection cycle. We have performed a genome-wide siRNA screen at biosafety level 4 that identifies 585 human proteins required for henipavirus infection. The host protein with the largest impact was fibrillarin, a nucleolar methyltransferase that was also required by measles, mumps and respiratory syncytial viruses for infection. While not required for cell entry, henipavirus RNA and protein syntheses were greatly impaired in cells lacking fibrillarin, suggesting a crucial role in the replication phase of infection. During infection, the Hendra virus matrix protein co-localized with fibrillarin in cell nucleoli, and by co-immunoprecipitation the two proteins interact. The methyltransferase activity of fibrillarin is required for henipavirus infection, suggesting this enzymatic activity could be targeted therapeutically to combat henipavirus infections.