Murray's 2-6 6-4 7-6 (7/1) victory over David Ferrer in the final of the Sony Open was enough to lift him above Roger Federer in the ATP rankings and into second place behind Novak Djokovic.
The Scot was last ranked at number two in September 2009, while it is the first time since November 2003 that neither Federer nor Rafael Nadal has been ranked inside the top two.
Meanwhile, Ferrer climbs back into the top four at the expense of Nadal, who, like Federer, did not play in Miami.
Murray's climb and Nadal's slip could have a big impact on the seedings for the French Open in May, although performances in the claycourt warm-up events will have a big say.
Having opted to skip this week's Davis Cup tie between Great Britain and Russia, which is being played on a hardcourt, the British star is already looking ahead to the first of those tournaments, the Monte Carlo Masters which gets under way on April 14.
"My focus now is on Monte Carlo. I'll take probably four days off and then start training here (in Miami) on clay," he told Sky Sports.
"Monte Carlo is next and I'll just keep trying to improve my clay game. I did a lot of things well this week but I need to serve better. I served poorly.
"If I'd served better I could have made it easier and that's something I need to do better in the clay court season. If I serve better I'll be able to win matches like this one more comfortably.
In the women's rankings, Serena Williams remains number one after winning the WTA title in Miami.
Briton Heather Watson falls one place to 40th, while compatriot Laura Robson climbs one to a career-high 42nd and could claim the top British ranking on the clay of Charleston this week.
Seeded 16th in a field headed by Williams, Robson faces Spain's Estrella Cabeza Candela in round one.
Anne Keothavong is back as British number three after winning an ITF tournament in France at the weekend. She is back inside the top 200 at 185th.