He defeated future world welterweight champion Carlos Palomino at the 1972 Olympic Trials, but lost to eventual gold medalist Sugar Ray Seales in the finals.
Ranzany knocked out Randy Shields on February 14, 1978, in the 11th round to earn the NABF welterweight title.
One year later, on August 12, 1979, Ranzany lost to Sugar Ray Leonard at Caesars Palace in Las Vegas, getting knocked out in the 4th round.
After this victory, Ranzany got one more shot at a premier welterweight, losing to Wilfred Benítez on December 12, 1980, in a 10-round unanimous decision.
On October 30, 1982, Ranzany defeated former lightweight champion Sean O'Grady in a 10-round unanimous decision.