  The neutral $B$ meson lifetime is measured with the data collected by the
BaBar detector at the PEP-II storage ring during the years 1999 and 2000, with
a total integrated luminosity of 20.7 ${\rm fb}^{-1}$. The decays $B^0 \to
D^{*-} \pi^+$ and $B^0 \to D^{*-} \rho^+$ are selected with a
partial-reconstruction technique, yielding samples of $6970 \pm 240$ and $5520
\pm 250$ signal events, respectively. With these events, the $B^0 $ lifetime is
measured to be $ 1.533 \pm 0.034 {\rm (stat.)} \pm 0.038 {\rm (syst.)} {\rm
ps}$. This measurement serves as a test and validation of procedures required
to measure the CP violation parameter $\sin(2\beta + \gamma)$ with partial
reconstruction of these modes.
