A compact and rugged sighting laser adapted to be mounted on the trigger guard of a firearm such as a handgun. The sighting laser includes a mounting block having a slot adapted to engage the trigger guard, and a housing configured to engage the mounting block. The mounting block includes a hardened retention pin disposed at one end of the block adjacent the slot, and the housing includes a rearward extending plate with a groove configured to receive this pin. The housing further defines first and second bores generally parallel to one another and oriented toward a forward end of the housing. A laser module is disposed in an ellipsoidally shaped casing that fits within the first housing bore, while a battery for the laser fits within the second bore. Threaded screws disposed at a forward end of the housing at right angles to one another press against one end of the ellipsoidal casing in order to provide orientation of the laser with respect to a target point of the firearm. A pair of activation switches are further disposed on opposing sides of the firearm to permit ambidextrous activation of the laser assembly. The switches may also be provided with extended bars to further facilitate one-fingered activation of the laser assembly.