With the advent of modern wide band telescopes, such as WSRT and the EVLA, Faraday rotation measure synthesis has become a valuable polarization technique. The construction of the Low FRequency ARray (LOFAR) opens up the opportunity to apply this technique to low frequencies. At LOFAR HBA frequencies, the resolution in Faraday space is typically sub 1 rad/m^2, allowing very precise measurements of Faraday depths. Unfortunately at these frequencies depolarization dramatically reduces the number of polarized sources, with some observations suggesting the number is as low as 1 source per 1.7 degrees. As such, targets for polarized study with LOFAR must be careful chosen. One promising class of targets for such studies are giant radio galaxies (GRGs), whose low density environments and high degree of intrinsic polarization minimize the effects of depolarization. Such objects are very interesting targets for polarized studies as, due to their large physical extent, observations of the Faraday effect can probe the magnetic fields in the extremely low density environments of the outer IGM and WHIM. Here we present the first detections of polarization in the GRG NGC 6251 at low frequencies (~150 MHz).We used the new polarization analysis techniques, RM synthesis and QU fitting, to study the environment of northern jet and lobe of NGC 6251.