In an entertaining start to the tournament, Wales banished memories of their defeat to Scotland in last year’s fixture with a commanding victory courtesy of tries from Gareth Davies and Steff Evans and Halfpenny’s double.
The experienced fullback added 14 points from the boot for a personal tally of 24.
Scotland had not won in Cardiff since 2002 but arrived in the Welsh capital buoyed up by a superb spell in November that saw them thump Australia and fall agonisingly short of a famous victory against the world champion All Blacks.
Wales, however -- without six British & Irish Lions stars -- started in inspired fashion at a fervent Principality Stadium with Davies intercepting a pass from opposite number Ali Price to canter over from 60 metres.
The visitors barely had time to settle in a breathless opening 15 minutes before Halfpenny dived over for his first Wales try since 2013 -- 38 games ago.
Scotland, one of the most dynamic and unpredictable attacking sides, were guilty of overplaying at times and found it difficult to build cohesion or put pressure on the Welsh defence.
Fielding a number of inexperienced players due to injury, Scotland made it to the break without falling further behind but any hopes of a second-half comeback were hampered by Halfpenny, who twice punished Scottish infringements to extend the lead.
Halfpenny then strolled over for his second on the hour mark and Evans scampered down the touchline to finish acrobatically in the closing stages, before two sweetly-struck conversions extended the fullback’s perfect record from the tee to six from six.
The only negative on a brilliant afternoon for Wales was Peter Horne’s late consolation try.
Wales finished above only Italy in last year’s championship but expertly marshalled the final 30 minutes and will be full of confidence when they travel to back-to-back champions England next Saturday.
Scotland -- tipped by many pundits to upset the dominance of tournament favourites England and Ireland -- host an unpredictable France in their next outing on Feb. 11.