The Kepler spacecraft has been monitoring the light from 150,000 stars in its primary quest to detect transiting exoplanets. Here, we report on the detection of an eclipsing stellar hierarchical triple, identified in the Kepler photometry. KOI-126 [A, (B, C)], is composed of a low-mass binary [masses M(B) = 0.2413 +/- 0.0030 solar mass (M(circle dot)), M(C) = 0.2127 +/- 0.0026 M(circle dot); radii R(B) = 0.2543 +/- 0.0014 solar radius (R(circle dot)), R(C) = 0.2318 +/- 0.0013 R(circle dot); orbital period P(1) = 1.76713 +/- 0.00019 days] on an eccentric orbit about a third star (mass M(A) = 1.347 +/- 0.032 M(circle dot); radius R(A) = 2.0254 +/- 0.0098 R(circle dot); period of orbit around the low-mass binary P(2) = 33.9214 +/- 0.0013 days; eccentricity of that orbit e(2) = 0.3043 +/- 0.0024). The low-mass pair probe the poorly sampled fully convective stellar domain offering a crucial benchmark for theoretical stellar models.