High-power giant pulses can be used applied in various applications with Q-switched micro-lasers. This method can shorten the pulse duration; however, active control is currently impossible in micro-lasers. To achieve precise pulse control while maintaining compactness and simplicity, we exploit the magneto-optical effect in magnetic garnet films with micromagnetic domains that can be actively controlled by a pulsed magnetic field. Our Q-switching technique enhances the output power by a factor of 4 × 103. Moreover, the device itself is smaller than other Q-switching devices. This novel type of active Q-switch can be combined with a micro-laser to obtain megawatt-order pulses.