The catalytic conversion of N2 to N(SiMe3)3 by homogeneous transition metal compounds is a rapidly developing field, yet few mechanistic details have been experimentally elucidated for 3 d element catalysts. Herein we show that Fe(PP)2(N2) (PP = R2PCH2CH2PR2; R = Me, 1Me; R = Et, 1Et) are highly effective for the catalytic production of N(SiMe3)3 from N2 (using KC8/Me3SiCl), with the yields being the highest reported to date for Fe-based catalysts. We propose that N2 fixation proceeds via electrophilic Nβ silylation and 1e- reduction to form unstable FeI(NN-SiMe3) intermediates, which disproportionate to 1Me/Et and hydrazido FeII[N-N(SiMe3)2] species (3Me/Et); the latter act as resting states on the catalytic cycle. Subsequent 2e- reduction of 3Me/Et leads to N-N scission and formation of [N(SiMe3)2]- and putative anionic Fe imido products. These mechanistic results are supported by both experiment and DFT calculations.