Photonic generation of linearly chirped microwave waveforms (LCMWs) using a monolithic integrated three-section laser is experimentally demonstrated in this work. All three sections of the laser cavity, including the front DFB section, phase section and rear DFB section, have the same active layer, which can avoid the butt-joint re-growth process. The gratings in both DFB sections are fabricated by the Reconstruction Equivalent Chirp technique, which can significantly decrease the difficulties in realizing precise grating structure. By adjusting the integrated three-section semiconductor laser to work in the period-one (P1) state and applying a sweeping signal to the front DFB section, the beating signal, i.e., an LCMW with a large time bandwidth product (TBWP), can be generated. In the current proof-of-concept experiment, an LCMW with a large TBWP up to 5.159 × 105 is generated, of which the bandwidth and the duration time are 6.7 GHz and 77 us respectively. The compressed pulse width is 150 ps. In addition, by adjusting the bias currents of the rear DFB section and front DFB section as well as the amplitude of the sweeping signals, LCMWs with tunable center frequency and tunable bandwidth can be achieved.