Significance When conduction electrons in a solid are completely spin polarized, the single-spin transport results in great promise in spintronic (i.e., spin electronic) applications. Realizing high-efficiency spintronic devices based on 2D van der Waals (vdW) materials would tremendously impact nanoscale spintronics and the current information technologies. However, a minority of vdW materials are magnetic, among which antiferromagnets do not have net spin polarization whereas ferromagnets usually have limited imbalance between oppositely polarized electrons. Here, we show that antiferromagnetic vdW bilayers can be made half metallic, in which electrons of singular spin are metallic but those of the opposite spin are insulating, leading to 100% spin-polarized conduction electrons. Based on this finding, an interesting type of spin field effect transistor is proposed.