The synthesis and structural determination of the first thorium phosphinidene complex are reported. The reaction of 2 equiv of (C5Me5)2Th(CH3)2 with H2P(2,4,6-iPr3C6H2) at 95 °C produces [(C5Me5)2Th]2(μ2-P[(2,6-CH2CHCH3)2-4-iPrC6H2] as well as 4 equiv of methane, 2 equiv from deprotonation of the phosphine and 2 equiv from C–H bond activation of one methyl group of each of the isopropyl groups at the 2- and 6-positions. Transition state calculations indicate that the steps in the mechanism are P–H, C–H, C–H, and then P–H bond activation to form the phosphinidene.