The aim of the Laser Megajoule facility (LMJ) is to deliver more than 1 MJ of laser energy to targets for high energy density physics experiments. In association with Greenfield Technology, we developed a specific timing system to synchronize the 176 laser beams on the target with a precision better than 40 ps rms and to trigger and mark plasma diagnostics. The final architecture, settled and used since three years, is based on a master oscillator that sends a clock with serial data through a fiber-optic network, allowing to synchronize more than 500 delay generators spread over the large LMJ facility. The settings of each laser beam and the various experiments require different sampling rates (multi to single shot) and 16 groups for coactivity. Three kinds of delay generators, electrical and optical, are designed for standard precision (<150 ps jitter) and the third is designed for high precision. Each output deliver trigger or fiducial signals with jitter down to 5 ps and peak-to-peak wander less than 10 ps over a week. Test performance of this LMJ timing system is in progress all over the LMJ facility. Besides it will be installed on the petawatt laser (PETAL) this year.