It was the first career title for the fourth-seeded Gasquet, who earned $53,000. The rising young star was playing in his second title match of 2005.
He was beaten by world No. 1 Roger Federer in last month's finale at the Hamburg Masters and was also was runner-up at Metz, France last season.
The 6-foot-5-inch Mirnyi, who was completely outplayed, was appearing in a championship match for the fourth time. It was his first-ever meeting with Gasquet, a grass-court specialist who is considered a threat at Wimbledon.
"It is great for me to prove I can play on the surface," Gasquet said after his win over Mirnyi. "Now I believe I can go a long way at Wimbledon next week."
Swim Week Miami Beach 2014 [PHOTOS]