The world number three opened the tournament with a four-under-par opening round of 68 and produced a stunning round of 64 at the halfway stage to move three shots clear of the field.
Westwood maintained his three-shot cushion on Friday and in the final round could even afford to miss five putts from inside six feet over the first 10 holes of his closing 69.
The 39-year-old Westwood finished on a 19-under-par total of 269, with fellow Englishman Fisher closing with a 71 to finish on 274.
Sergio Garcia’s closing 67 was the best round of the day and moved the Spaniard up to a share of third place on 275 alongside Finn Mikko Ilonen and Sweden’s Peter Hanson.
It was Westwood’s first victory since the Ballantine’s Championship in May 2011 and came nearly four months after his runner-up place at the Dubai Desert Classic.
The Scandinavian Masters has its origins in the late 1960s and is currently the only European Tour event to be held in Scandinavia.
The event is traditionally held at the end of July/beginning of August but was moved in 2012 to allow the players more time to travel to the upcoming U.S. Open.
Three of the last four tournaments have been one by Swedes prior to Westwood’s success, with Argentinian Ricardo Gonzalez the home player dominance in 2009.