  Since the first discovery of a broad-lined type Ic supernova (SN) with a
long-duration gamma-ray burst (GRB) in 1998, fewer than fifty gamma-ray burst
supernovae (GRB-SNe) have been discovered. The intermediate-luminosity Swift
GRB 161219B and its associated supernova SN 2016jca, which occurred at a
redshift of z=0.1475, represents only the seventh GRB-SN to have been
discovered within 1 Gpc, and hence provides an excellent opportunity to
investigate the observational and physical properties of these very elusive and
rare type of SN. As such, we present optical to near-infrared photometry and
optical spectroscopy of GRB 161219B and SN 2016jca, spanning the first three
months since its discovery. GRB 161219B exploded in the disk of an edge-on
spiral galaxy at a projected distance of 3.4 kpc from the galactic centre. GRB
161219B itself is an outlier of the Amati relation, while SN 2016jca had a
rest-frame, peak absolute V-band magnitude of M_V = -19.0, which it reached
after 12.5 rest-frame days. We find that the bolometric properties of SN
2016jca are inconsistent with being powered solely by a magnetar central
engine, as proposed by other authors, and demonstrate that it was likely
powered exclusively by energy deposited by the radioactive decay of nickel and
cobalt into their daughter products, which were nucleosynthesized when its
progenitor underwent core collapse. We find that 0.22 solar masses of nickel is
required to reproduce the peak luminosity of SN 2016jca, and we constrain an
ejecta mass of 5.8 solar masses and a kinetic energy of ~5 x 10^52 erg.
Finally, we report on a chromatic, pre-maximum bump in the g-band light curve,
and discuss its possible origin. [Abridged]
