We report the discovery of 1RXS J173006.4+033813 , a polar cataclysmic variable with a period of 120.21 min .
The white dwarf primary has a magnetic field of B = 42 ^ { +6 } _ { -5 } { MG } , and the secondary is a M3 dwarf .
The system shows highly symmetric double peaked photometric modulation in the active state as well as in quiescence .
These arise from a combination of cyclotron beaming and ellipsoidal modulation .
The projected orbital velocity of the secondary is K _ { 2 } = 390 \pm 4 { km s } ^ { -1 } .
We place an upper limit of 830 \pm 65 { pc } on the distance .