Welsh centre Jamie Roberts - facing Australia for the first time this summer due to injury - has scored the Lions' fourth try, taking a pass from replacement Conor Murray before galloping home.
Halfpenny makes it another seven points, and the Lions start to celebrate a series win.
More top news
It will be cloudy with outbreaks of rain at first, but most of the rain will clear by morning.
Despite leading at half time, Howley's men failed to score in the second half with Scotland racking up 20 points to seal the win.
It's half time at Murrayfield and Wales are leading at half time, thanks to Liam Williams' third try of the tournament.