  Using high-resolution spectra from the Tillinghast Reflector Echelle
Spectrograph (TRES) and photometry from sector 56 of the Transiting Exoplanet
Survey Satellite (TESS), we report that the nearby M dwarf G 68-34 is a
double-lined eclipsing binary. The pair is spin-orbit synchronized with a
period of 0.655 days. The light curve shows significant spot modulation with a
larger photometric amplitude than that of the grazing eclipses. We perform a
joint fit to the spectroscopic and photometric data, obtaining masses of
$0.3280\pm 0.0034$M$_\odot$ and $0.3207\pm 0.0036$M$_\odot$ and radii of
$0.345\pm 0.014$R$_\odot$ and $0.342\pm 0.014$R$_\odot$ after marginalizing
over unknowns in the starspot distribution. This system adds to the small but
growing population of fully convective M dwarfs with precisely measured masses
and radii that can be used to test models of stellar structure. The pair also
has a white dwarf primary at 9" separation, with the system known to be older
than 5 Gyr from the white-dwarf cooling age. The binarity of G 68-34 confirms
our hypothesis from Pass et al. (2022): in that work, we noted that G 68-34 was
both rapidly rotating and old, highly unusual given our understanding of the
spindown of M dwarfs, and that a close binary companion may be responsible.
