  The X-ray binary 4U 1543$-$624 has been provisionally identified as an
ultracompact system with an orbital period of $\simeq$18~min. We have carried
out time-resolved optical imaging of the binary to verify the ultra-short
orbital period. Using 140\,min of high-cadence $r'$-band photometry we recover
the previously-seen sinusoidal modulation and determine a period
$P=18.20\pm0.09$\,min. In addition, we also see a 7.0$\times
10^{-4}$\,mag\,min$^{-1}$ linear decay, likely related to variations in the
source's accretion activity. Assuming that the sinusoidal modulation arises
from X-ray heating of the inner face of the companion star, we estimate a
distance of 6.0--6.7\,kpc and an inclination angle of
34$^{\circ}$--61$^{\circ}$ (90\% confidence) for the binary. Given the
stability of the modulation we can confirm that the modulation is orbital in
origin and 4U 1543$-$624 is an ultracompact X-ray binary.
