Clemente played eighteen seasons in Major League Baseball from 1955 to 1972, all with Pittsburgh. He was awarded the National League’s Most Valuable Player Award in 1966. During the course of his career, Clemente was selected to participate in the league's All Star Game on twelve occasions. He won twelve Gold Glove Awards and led the league in batting average four different seasons. He was involved in charity work both in Puerto Rico and other Latin American countries, often delivering baseball equipment and food to them. He died in an aviation accident on December 31, 1972, while en route to deliver aid to earthquake victims in Nicaragua. His body was never recovered. He was elected to the Hall of Fame posthumously in 1973, thus becoming the first Latin American to be selected and the only current Hall of Famer for whom the mandatory five year waiting period was waived since the wait was instituted in 1954.
During the middle of the season, Clemente was involved in a car accident; this caused him to miss several games with an injury in his lower back. He finished his rookie season with an average of .255, despite confronting trouble hitting certain types of pitches. His defensive skills, however, were highlighted during this season. During the off season, Clemente played with the Santurce Crabbers in the Puerto Rican baseball winter league, where he was already considered a star.
He remained in the reserves until September 1964. Early in the 1960 season, Clemente led the league, batting an average of .353 and scoring Runs Batted In (RBIs) in twenty-five out of twenty-seven games. Roberto's batting average stayed above the .300 mark throughout the course of the campaign. In August, he was inactive for five games as a result of an injury on his chin; he received this injury when his head impacted a concrete wall while he was trying to catch a hard line hit that reached the park's outer wall. Following this accident, he was transported to a local hospital, where the doctors stitched his chin; this prohibited him from playing until the injury was healed. The Pirates compiled a 95-59 record during the regular season, winning the National League pennant, and defeated the New York Yankees in a seven-game World Series. Clemente batted .310 in the series, hitting safely at least once in every game. His .314 batting average, 16 home runs, and defense during the course of the season earned him his first participation in the All-Star game, where he served as a reserve player.
During the 1961 spring training, Clemente tried to modify his batting technique by using a heavier bat in order to slow the speed of his swing, following advice from Pirates' batting coach George Sisler. During the 1961 season, Clemente was selected as the starting right fielder for the National League in the All-Star game. In this game, he batted a triple on his first at-bat and scored the team's first run. With the American League ahead 4-3 in the tenth inning, Clemente hit a double that gave the National League a decisive 5-4 win.
Following the season, he traveled to Puerto Rico along with Orlando Cepeda, who was a native of Ponce. When both players arrived, they were received by 18,000 people, who were celebrating that this was the first season in which both leagues in Major League Baseball were led in batting average by Puerto Rican players. On November 14, 1964, Clemente married Vera Zabala. The ceremony took place in the church of San Fernando in Carolina and was attended by thousands of fanatics. During this time, he was also involved in managing the Senadores de San Juan in the LBPPR, as well as playing with the team during the Major League offseason. During the course of the winter league, Clemente was injured and only participated as a pinch hitter in the league's All-Star game. He experienced a complication on his injury during the course of this game and underwent surgery shortly after being carried off of the playing field.
This condition limited his role with the Pirates in the first half of the 1965 season, during which he batted an average of .257. He was inactive for several games during this stage of the campaign before being fully active; when he returned to the starting lineup, he hit in thirty-three out of thirty-four games and his average improved to .340. Roberto and Vera had their first son on August 17, 1965, when Roberto Clemente, Jr. was born; he was the first of three children, along with Luis Roberto and Enrique Roberto. During the 1960s, he batted over .300 in every year except 1968, when he hit .291. He was selected to every All-Star game, and he was given a Gold Glove every season from 1961 onwards. He led the National League in batting average four times (1961, 1964, 1965, and 1967), led the National League in hits twice (1964 and 1967), and won the Most Valuable Player award in the 1966 season, when he hit .317 while setting career highs in home runs (29) and RBI (119). In 1967, he registered a career high .357 average and hit twenty-three home runs and 110 runs batted in.
In the 1971 season, the Pirates won the National League and faced the Baltimore Orioles in the World Series. Baltimore had won 100 games and swept the American League Championship Series, both for the third consecutive year, and were the defending World Series champions. The Orioles won the first two games in the series, but Pittsburgh won the championship in seven games. This marked the second occasion that Clemente had won a World Series with the Pirates. Over the course of the series, Clemente batted a .414 average (12 hits in 29 at-bats), performed well defensively, and hit a solo home run in the deciding 2-1 seventh game victory. Following the conclusion of the season, he received the World Series Most Valuable Player award. Struggling with injuries, Clemente only managed to appear in 102 games in 1972, but he still hit .312 for his final .300 season. On September 30,, in a game at Three Rivers Stadium, he hit a double off Jon Matlack of the New York Mets for his 3,000th hit. It was the last at-bat of his career during a regular season, though he did play in the 1972 NLCS playoffs against the Cincinnati Reds. In the playoffs, he batted .235 as he went 4 for 17. His last game ever was at Cincinnati's Riverfront Stadium in the fifth game of the playoff series.
Clemente decided to accompany the fourth relief flight, hoping that his presence would ensure that the aid would be delivered to the survivors. The airplane he chartered for a New Year's Eve flight, a Douglas DC-7, had a history of mechanical problems and sub-par flight personnel, and it was overloaded by 5,000 pounds. It crashed into the ocean off the coast of Isla Verde, Puerto Rico immediately after takeoff on December 31, 1972. A few days after the crash, the body of the pilot and part of the fuselage of the plane were found. An empty flight case apparently belonging to Clemente was the only personal item recovered from the plane. Teammate Manny Sanguillen, a catcher and Clemente's best friend, was the only member of the Pirates not to attend Roberto's funeral. He chose instead to dive into the waters where Clemente's plane had crashed in an effort to find his teammate. Clemente's body was never recovered.
At the time of his death, Clemente had established several records within the Pittsburgh Pirates, including possessing the record for hitting the most triples in a single game with three and the record for most hits in two consecutive games with ten, as well as achieving other accomplishments that were unparalleled at the moment. These include tying the record for most Gold Glove Awards won among outfielders with twelve, which he shares with Willie Mays. He also became the only player to have ever hit a walk-off inside-the-park grand slam. He accomplished this historic feat on July 25, 1956 in a 9-8 Pittsburgh win against the Chicago Cubs, at Forbes Field. In addition, he was one of four players to have ten or more Gold Gloves and a lifetime batting average of over .300.
On March 20, 1973, the Baseball Writers Association of America held a special election for the Baseball Hall of Fame. They voted to waive the waiting period for Clemente, due to the circumstances of his death, and posthumously elected him for induction into the Hall of Fame, giving him 393 of the 420 available votes, or 92% of the vote. Clemente's Hall of Fame plaque had originally read "Roberto Walker Clemente". In 2000, the plaque was recast to express his name in the proper Hispanic format, "Roberto Clemente Walker".
MLB presents the Roberto Clemente Award every year to the player who best follows Clemente's example with humanitarian work. Clemente was awarded the Congressional Gold Medal in 1973 and the Presidential Medal of Freedom in 2002. In 2003, he was inducted into the United States Marine Corps Sports Hall of Fame. On October 26, 2005, Clemente was named a member of Major League Baseball's Latino Legends Team. At the Major League Baseball All-Star game in Pittsburgh, Pennsylvania on July 11, 2006, many of the players on both teams wore yellow wristbands with the initials "RCW" in honor of Clemente. At the end of the fourth inning, Clemente was awarded the Commissioner's Historical Achievement Award by the Commissioner of Baseball; the award was accepted by his widow. During the award presentation, the Commissioner of Baseball Bud Selig stated that "Roberto was a hero in every sense of the word". PNC Park, the home ballpark of the Pirates which opened in 2001, includes a right field wall high, in reference to Clemente's uniform number and his normal fielding position during his years with the Pirates.
Puerto Rico has honored Clemente's memory by naming the coliseum in San Juan the Roberto Clemente Coliseum; two baseball parks are in Carolina, the professional one , Roberto Clemente Stadium, and the Double-A. There is also the Escuela de los Deportes (School of Sports) that has the Double-A baseball park and the number 21 can't be used in any of the baseball teams there.. Today, this sports complex is called Ciudad Deportiva Roberto Clemente. In Pittsburgh, the 6th Street Bridge was renamed in his memory, and the Pirates retired his number 21 at the start of the 1973 season. The City of Pittsburgh maintains Roberto Clemente Memorial Park along North Shore Drive in the city's North Side. In 2007, the Roberto Clemente Museum opened in the Lawrenceville section of Pittsburgh. Some schools, such as Roberto Clemente High School in Chicago, Illinois and the Roberto Clemente Charter School in Allentown, Pennsylvania, were named in Clemente's honor.
On August 17, 1984, the day before what would have been his 50th birthday, the United States Postal Service issued a postage stamp honoring Clemente. Designed by Juan Lopez-Bonilla, the spare clean design shows Clemente wearing his Pirates cap, with the Puerto Rican flag in the background. In 1999, he ranked Number 20 on The Sporting News' list of the 100 Greatest Baseball Players, the highest-ranking Latino player on the list. Later that year, Clemente was nominated as a finalist for the Major League Baseball All-Century Team.