Luis Alvarado was born on January 15, 1949, in Lajas, Puerto Rico where he attended the Luis Muñoz Rivera high school. He began playing baseball at the age of 12 with the Police Athletic League.

He played amateur ball in Puerto Rico with Class-A teams La Parguera and Palmarejo Tigers and in Double-A, the highest local level, he was with the Aibonito Polluelos. At age 17, he joined the San Juan Senators of the Puerto Rico Winter League. While still a teenager, he signed with the Boston Red Sox.

The year he turned 18, 1967, he played for the Waterloo (Iowa) Hawks in the Single-A Midwest League. Over the winter of 1967-68, he first played for San Juan and was named the PRWL’s Rookie of the Year. 

Luis got his first taste of the majors in the spring of 1968. He was brought to camp with the Red Sox and was the youngest player on any AL team’s major-league roster. He truly impressed with his slick and sensational fielding. Manager Dick Williams said that he was the surprise of the camp and that he would be a player to protect in the expansion draft that. But Luis was still in need of seasoning and was sent to the Pittsfield Red Sox of the Double-A Eastern League.

The Red Sox called him up when rosters expanded, and in September 1968, he made his major-league debut against the Minnesota Twins at Fenway Park. Rico Petrocelli was out with an injured wrist, so Luis played in each of the next 10 games, going 6-for-46 (.130 BA) with one RBI. 

For most of the 1969 season, he played in Triple A for the Louisville Colonels and once again, he was brought up to the majors in September. While with the Red Sox, he learned he had been named International League Rookie of the Year.

In 1970, Luis made the big club out of spring training. Eddie Kasko had taken over as Red Sox skipper and there was a lengthy debate regarding Alvarado and Petrocelli, and who should play third base or shortstop. Alvarado, still only 21 years old, played third base steadily from Opening Day through June, but was benched because he was then batting .235, had driven in only two runs, and George Scott was then returned to play third base.

Luis was sent to Louisville where he struggled badly, batting only .201 in 69 games. He was called back up in early September and appeared in 11 games, going 3-for-21. 

In December, the Red Sox traded Luis and the popular Mike Andrews to Chicago, for 36-year-old Luis Aparicio. Luis joined the White Sox at Sarasota for spring training in 1971 and became the regular shortstop, but by season’s end, he had hit only .216. In 1972, playing part time, he batted .213 and in 1973, he was only used as a utility infielder.

In 1974, he was a man on the move. After getting one hit in 10 games for the White Sox, he was traded to the St. Louis Cardinals in April. Then after hitting .139 in 17 games for the Cardinals, he was dealt in June, to the Cleveland Indians.

He spent the entire 1975 season in Triple-A ball. He played first for Oklahoma City (a Cleveland affiliate) and then Tulsa (a Cardinals affiliate, also in the American Association). 

He aspent most of 1976 with the Tulsa Oilers, and had his best season of pro ball. In Septembe, he was called up to St. Louis and got into 16 games.

In an eight-month stretch, he was part of four transactions. His contract was sold to the Detroit Tigers in November, 1976. In March, the Tigers sold his contract to the New York Mets on a conditional basis. In April, the Tigers asked for him back, repurchasing his contract. For the Tigers, he played briefly at the end of two April games in 1977, having one at-bat and was released in June. Luis turned down the Tigers’ offer to play for their Triple-A team in Evansville.

In August 1977, he joined the Hawaii Islanders as a free agent. His other PRWL championship came in 1977-78 with Mayagüez. He moved on to Ponce for the 1978-79 campaign, and partway through the winter of 1980-81, he went from Ponce to Arecibo. In the summers from 1979 through 1981, he played in the Mexican League.

After he retired from professional baseball, he accepted a job with the Lajas Municipality, his native city and hometown, as a sports and recreational leader. He also kept active in the community managing some Little League baseball teams and also owned two small markets in Lajas. 

Luis Alvarado died from a heart attack while coaching a basketball game, at age 52, on March 20, 2001, in Lajas, Puerto Rico.