A fastener attaching tool particularly suited for use in attaching buttons to clothing, etc. and which is constructed for use with a fastener clip which includes a pair of runner bars and one or more U-shaped fasteners having transverse bars at opposite ends, each transverse bar being connected on its side to a corresponding runner bar by a severable connector post. The tool includes a pair of needles each having a longitudinal slotted bore adapted to receive one of the transverse bars and a knife edge formed on one side which is adapted to sever a connector post from its associated transverse bar as the transverse bar is pushed through the needle. The body includes a transverse feed slot disposed just to the rear of the needles down through which the fastener clip is manually inserted. The tool also includes an ejector mechanism, which is slidably mounted back and forth within the body and is rearwardly biased by a spring. The ejector mechanism is manually operable from the rear of the body and includes a pair of ejector rods which are slidably back and forth within the bores of the needles and are used to push the transverse bars into and through the needles.