A fuel cell gas diffusion layer includes: a porous carbon fiber base substrate containing discontinuous carbon fibers bonded to each other with carbide, and a porous layer containing at least carbonaceous particles, the porous carbon fiber base substrate having a porous layer (A) with a mean thickness t1 of 10 to 55 μm deposited on one surface A thereof, the porous carbon fiber base substrate being impregnated with porous layer (J) at least part of which is exposed at an opposite surface B, the porous carbon fiber base substrate having internal pores with a cross-sectional area accounting for 5% to 40% of the total cross section in a through-plane direction, at least porous layer (A) and porous layer (J) both having a void percentage of 50% to 85%, the porous carbon fiber base substrate having a thickness of 60 to 300 μm, and the porous carbon fiber base substrate having a bulk density of 0.20 to 0.45 g/cm3.