  We report the discovery of an L dwarf companion to the A3V star \beta{}
Circini. VVV J151721.49-585131.5, or \beta{} Cir B, was identified in a proper
motion and parallax catalogue of the Vista Variables in the V\'{i}a L\'{a}ctea
survey as having near infrared luminosity and colour indicative of an early L
dwarf, and a proper motion and parallax consistent with that of \beta{} Cir.
The projected separation of $\sim$3.6' corresponds to $6656$ au, which is
unusually wide. The most recent published estimate of the age of the primary
combined with our own estimate based on newer isochrones yields an age of
$370-500$ Myr. The system therefore serves as a useful benchmark at an age
greater than that of the Pleiades brown dwarfs and most other young L dwarf
benchmarks. We have obtained a medium resolution echelle spectrum of the
companion which indicates a spectral type of L1.0$\pm$0.5 and lacks the typical
signatures of low surface gravity seen in younger brown dwarfs. This suggests
that signs of low surface gravity disappear from the spectra of early L dwarfs
by an age of $\sim370-500$ Myr, as expected from theoretical isochrones. The
mass of \beta{} Cir B is estimated from the BHAC15 isochrones as
$0.056\pm0.007$ M$_{\odot}$.
