A growing number of focused ultrasound (FUS) therapies use low intensity FUS with microbubbles to induce mechanical bioeffects for the non-invasive treatment of localized tissue regions. For these low intensity mechanical-based FUS therapies, there is a need for therapy planning and real-time monitoring techniques to ensure that the FUS beam is targeted to the desired region even in the presence of tissue motion. In this work, a system is presented for combined therapy planning, low intensity FUS treatment, and real-time therapy monitoring using a single diagnostic imaging array. First, a sonication pattern was determined by manually segmenting the treatment region from a B-mode image captured with the imaging array. To visualize the FUS therapy beam, a focused pulse excitation was transmitted and backscattered signals were used to reconstruct the intensity field of the FUS beam. The FUS beam reconstruction was overlaid onto a co-aligned B-mode image captured with the imaging array, allowing one to qualitatively monitor the position and size of the FUS beam with anatomical context from the B-mode image. Real-time beam visualizations at a frame rate of 25-30 frames per second were achieved in a rat tumor in vivo and a mock FUS therapy was planned and monitored in a tissue-mimicking phantom.