  In addition to being the most magnetic objects in the known universe,
magnetars are the only objects observed to generate fast-radio-burst-like
emissions. The formation mechanism of magnetars is still highly debated, and
may potentially be probed with the magnetar velocity distribution. We carried
out a 3-year-long astrometric campaign on Swift J1818.0-1607 -- the
fastest-spinning magnetar, using the Very Long Baseline Array. After applying
the phase-calibrating 1D interpolation strategy, we obtained a small proper
motion of 8.5 $\mathrm{mas~yr^{-1}}$ magnitude, and a parallax of $0.12\pm0.02$
mas (uncertainties at $1\,\sigma$ confidence throughout the Letter) for Swift
J1818.0-1607. The latter is the second magnetar parallax, and is among the
smallest neutron star parallaxes ever determined. From the parallax, we derived
the distance $9.4^{+2.0}_{-1.6}$ kpc, which locates Swift J1818.0-1607 at the
far side of the Galactic central region. Combined with the distance, the small
proper motion leads to a transverse peculiar velocity $v_\perp=48^{+50}_{-16}$
$\mathrm{km~s^{-1}}$ -- a new lower limit to magnetar $v_\perp$. Incorporating
previous $v_\perp$ estimates of seven other magnetars, we acquired
$v_\perp=149^{+132}_{-68}$ $\mathrm{km~s^{-1}}$ for the sample of
astrometrically studied magnetars, corresponding to the three-dimensional space
velocity $\sim190^{+168}_{-87}$ $\mathrm{km~s^{-1}}$, smaller than the average
level of young pulsars. Additionally, we found that the magnetar velocity
sample does not follow the unimodal young pulsar velocity distribution reported
by Hobbs et al. at $>2\,\sigma$ confidence, while loosely agreeing with more
recent bimodal young pulsar velocity distributions derived from relatively
small samples of quality astrometric determinations.
