BaNa2Fe[VO4](2) contains a Jahn-Teller active ion (Fe-II, 3d(6), high-spin) in an octahedral coordination. On the basis of a combination of temperature-dependent X-ray diffraction and Mossbauer and Raman spectroscopies, we demonstrate the coupling of lattice dynamics with the electronic ground state of Fe-II. We identify three lattice modes combined to an effective canted screw-type motion that drives the structural transition around room temperature from the high-temperature (P (3) over bar) via intermediate phases to the low temperature phase (C2/c). The dynamics of the electronic ground state of Fe(II) are evident from Mossbauer data with signatures of a motion-narrowed doublet above 320 K, a gradual evolution of the E-5 electronic state below 293 K, and finally the signature of the thermodynamically preferred orbitally nondegenerate ground state ((5)A(g)) of Fe(II) below 100 K. The continuous nature of the transition is associated with the temperature-dependent phonon parameters derived from Raman spectroscopy, which point out the presence of strong electron phonon coupling in this compound. We present a microscopic mechanism and evaluate the collective component leading to the structural phase transition.