The Henipavirus genome is encapsidated by the nucleoprotein (N) within a helical nucleocapsid that recruits the polymerase complex via the phosphoprotein (P). In a previous study, we reported that in henipaviruses, the N-terminal domain of the phosphoprotein and the C-terminal domain of the nucleoprotein (N$_{TAIL}$) are both intrinsically disordered. Here we show that Henipavirus N$_{TAIL}$ domains are also disordered in the context of full-length nucleoproteins. We also report the cloning, purification, and characterization of the C-terminal X domains (P$_{XD}$) of Henipavirus phosphoproteins. Using isothermal titration calorimetry, we show that N$_{TAIL}$ and P$_{XD}$ form a 1:1 stoichiometric complex that is stable under NaCl concentrations as high as 1 m and has a KD in the μm range. Using far-UV circular dichroism and nuclear magnetic resonance, we show that PN$_{XD}$ triggers an increase in the α-helical content of N$_{TAIL}$. Using fluorescence spectroscopy, we show that PXD has no impact on the chemical environment of a Trp residue introduced at position 527 of the Henipavirus N$_{TAIL}$ domain, thus arguing for the lack of stable contacts between the C termini of NTAIL and P$_{XD}$. Finally, we present a tentative structural model of the N$_{TAIL}$-P$_{XD}$ interaction in which a short, order-prone region of NTAIL (α-MoRE; amino acids 473–493) adopts an α-helical conformation and is embedded between helices α2 and α3 of P$_{XD}$, leading to a relatively small interface dominated by hydrophobic contacts. The present results provide the first detailed experimental characterization of the N-P interaction in henipaviruses and designate the N$_{TAIL}$-P$_{XD}$ interaction as a valuable target for rational antiviral approaches.