Generation of ultra-short high brightness electron bunches, suitable for injection into single pass Free Electron Lasers or Laser Wakefield Accelerators requires accelerating fields > 1 GV/m. To generate such fields a 2.5 MV sub-nanosecond pulser was built and tested. The pulser is based on a Tesla transformer with an output voltage of up to 2.5 MV. The output pulse is transferred through a laser triggered spark gap to a pulse forming line. The spark gap is triggered using a 5 ns (frequency doubled Nd:Yag) laser pulse, resulting in a jitter of 5 ns at the end of the line. The pulse forming line after the Tesla transformer was tuned to allow accurate shaping of the pulse. The output pulse of the system has a duration of 1 nanosecond and a risetime of approximately 150 ps. The output voltage can be varied and a maximum pulse height of 2.4 MV was achieved.