  The four-color ($B$ $V$ $R_c$ $I_c$) light curves of V776 Cas are presented
and analyzed using the Wilson-Devinney (W-D) method. It is discovered that V776
Cas is an early F-type (F2V) overcontact binary with a very high contact degree
($ f=64.6\,\%$) and an extremely low mass ratio ($q=0.130$), which indicate
that it is at the final evolutionary stage of cool short-period binaries. The
mass of the primary and secondary stars are calculated to be $M_1 =
1.55(\pm0.04)M_\odot$, $M_2 = 0.20(\pm0.01)M_\odot$. V776 Cas is supposed to be
formed from an initially detached binary system via the loss of angular
momentum due to the magnetic wind. The initial mass of the present primary and
secondary components are calculated to be $M_{1i} = 0.86(\pm0.10)M_\odot$ and
$M_{2i} = 2.13(\pm0.04)M_\odot$. The observed-calculated ($O$-$C$) curve
exhibits a cyclic period variation, which is due to the light-travel time
effect (LTTE) caused by the presence of a third component with a period of 23.7
years. The mass of the third component is estimated to be $M_3 =
1.04(\pm0.03)M_\odot$ and the orbital inclination of the third component is
calculated to be $i' = 33.1^{\circ}$. The distance of the binary system to the
mass center of the triple system is calculated to be $a'_{12} = 3.45AU$. The
presence of the close-in tertiary component may play an important role in the
formation and evolution of this binary system by drawing angular momentum from
the central system.
