United won the International Champions Cup courtesy of a 3-1 win over Premier League rivals Liverpool, putting in an impressive second half display following an unconvincing performance before the break.
Wayne Rooney - who was awarded Player of the tournament - was handed the armband by the Dutchman for the final in Miami and the England striker led by example, grabbing his side's equaliser before Juan Mata scored what proved to be the winning goal moments later - with Jesse Lingard sealing the victory.
Van Gaal has made a big impression since taking over the reins at Old Trafford, with a number of first team stars coming out to praise the 62-year-old's methods, and the team has already shown significant signs of improvement from last term on their pre-season tour in the US.
LA Galaxy were blown away in Van Gaal's first game in charge, with the MLS outfit thumped 7-0 in a match before the tournament got underway, and United have remained unbeaten under their new boss.
Having beaten Roma 3-2 and seen off fellow Serie A side Inter on penalties following a 0-0 draw, United then beat Real Madrid in front of a record crowd to secure their place in the final against Liverpool.
Van Gaal has stated he wants to win a major trophy in his first season at Manchester United, and has laid down a marker with their pre-season success.