Marrero, who played for the Washington Senators, was two days short of his 103rd birthday. He had been in declining health for weeks and was unresponsive for some time on Wednesday before dying, his grandson Rogelio Marrero said.
After an outstanding career in Cuba in the 1930s and 1940s, Marrero debuted in the Major Leagues with Washington in 1950, four days before his 39th birthday. He quickly became a wisecracking cult hero, with an elaborate windup, thick Cuban accent and ever-present cigar.
Smart and funny, he lacked a good fastball but got Major League hitters out by changing speeds and hitting spots with his slider, a relatively rare pitch in those days. He was highly regarded in Cuba for choosing to stay in the country after the 1959 revolution that brought Fidel Castro to power.
Though mostly bedridden since breaking his hip in 2011, Marrero kept chewing on cigars until his final days.
"He still takes his cigars and red wine, and if I brought him women he'd take that, too," Rogelio Marrero said in March. "Those were always his great vices."
The oldest living former major leaguer is now Mike Sandlock, 98, who played for the Boston Braves, Brooklyn Dodgers and Pittsburgh Pirates between 1942 and 1953.
Author and Cuban baseball expert Peter Bjarkman said when he first met Marrero in 1999, the former ballplayer, then in his late 80s, was sitting by the pool at nine in the morning, drinking rum and smoking a cigar.
"He was just an exceptional case, a legend," said Cuban baseball writer Sigfredo Barros, who puts Marrero in a pantheon with such Cuban baseball greats as Adolfo Luque, Martin Dihigo, Minnie Miñoso and Omar Linares.
"How is it possible that a man arrives in the Major Leagues at 38 or 39 years old, standing 5-foot-6 (1.68 meters), with short arms and small hands, and goes on to win 39 games for a team that was terrible?" Barros asked rhetorically.
At first dismissed as a joke for the usually hapless Senators, Marrero made believers by striking out great hitters such as Ted Williams, Joe DiMaggio and Mickey Mantle. Major League players took to calling him "Connie," though he was always Conrado in Cuba.
"Connie Marrero had a windup that looked like a cross between a windmill gone berserk and a mallard duck trying to fly backwards," former player and manager Felipe Alou wrote in his 1967 autobiography.
Marrero was one of only a few players to make the all-star team for the first time past the age of 40.
He pitched five seasons until he was 43, ending his big league career with a record of 39-40 and an earned run average (ERA) of 3.67. His ERA was better than the league average in all but his final season.
He failed to qualify for a baseball pension, but the Major League Baseball Players Association, the players' union, decided to compensate him under a program for players who came up short of the required service time. The union said it had to overcome numerous obstacles related to the U.S. economic embargo of Cuba for Marrero to get his money.
He made his name in Cuba playing for the Cienfuegos franchise and helped the national team win the Baseball World Cup three times in the 1940s, Barros said.
A ROOKIE PAST HIS PRIME
Marrero started pitching in the U.S.-based Florida International League in his 30s after he was suspended in Cuba for playing for more than one team. His minor league team, the Havana Cubans, was affiliated with the Washington Senators.
"I asked him once, 'If I wanted to see you at your best, when should I have seen you?' He said 1938. So 12 years after his peak, he arrived in the big leagues," said Kit Krieger, a Canadian friend of Marrero's and an expert on Cuban baseball.
As was custom at the time, monolingual sports writers would mock his accent, spelling words phonetically in his quotes.
During spring training ahead of the 1950 season, Senators manager Bucky Harris was incredulous at first that owner Clark Griffith signed Marrero, calling him "another Cuban joke," Krieger said.
That "joke" made the American League all-star team a year later.
Marrero became the elder statesman of the Caribbean island's national sport, still serving as a coach in uniform with the Granma team until his mid-90s.
He was chosen to throw out the ceremonial first pitch in a landmark 1999 exhibition game in Havana between the Cuban national team and the Baltimore Orioles.
Even as he passed 100 years, he liked to relax in an easy chair, listening to ball games on the radio with a cigar in his left hand, a baseball in his right.