Patek was drafted by the Pittsburgh Pirates in the 22nd round of the 1965 Major League Baseball draft out of Seguin High School in Seguin, Texas. He made his major league debut on June 3, 1968 against the Los Angeles Dodgers at short, and played all but six of his 292 games with the Pirates at short. However, with All-Star Gene Alley firmly entrenched at shortstop there was a desire on the part of management to convert him into a utility player.
Following the 1970 season, the Pirates dealt Patek, Bruce Dal Canton and Jerry May to the Kansas City Royals for Jim Campanis, Jackie Hernandez and Bob Johnson. In his first season with the Royals, Patek hit for the cycle on July 9, 1971, and led the American League with eleven triples to finish sixth in A.L. M.V.P. balloting. He earned his first of three All-Star selections the following season, and was a staple of the Royals line-up that won the American League West from 1976 through 1978. He led the American League with 53 stolen bases in 1977. A memorable image was captured by NBC-TV of Patek sitting painfully alone in the Royals' empty dugout while the New York Yankees celebrated on-field their come-from-behind victory to win the last game of the 1977 American League Championship Series, played in Kansas City on Patek's 33rd birthday. The game and series ended when Patek grounded into a double play.
Following the 1979 season, Patek signed as a free agent with the California Angels. He became the second shortstop, after Ernie Banks, to hit three home runs in a single game on June 20, 1980 against the Boston Red Sox at Fenway Park. In 1981, Patek was relegated to a utility role, actually seeing more playing time backing up Bobby Grich at second base than he did at short.
Patek retired after the 1981 season with a career batting average of .242. Patek was better known for his speed and his defensive abilities; former manager Whitey Herzog called Patek the best artificial turf shortstop he ever managed, ranking him even higher than Ozzie Smith.
When asked by a reporter what it felt like to be the smallest player in the major leagues, Patek replied- "I'd rather be the smallest player in the majors than the tallest player in the minors."
Although Patek played in four American League Championship Series, his teams never reached the World Series. The Pirates won the World Series the season after Patek left the Pirates (1971), and the Royals lost the World Series the season after Patek left the Royals (1980). Baseball analyst Bill James has ranked Patek, a member of the Kansas City Royals Hall of Fame, the 14th best player in Royals' history.
Patek briefly served as a part-time baseball analyst for NBC after his retirement.
On July 21, 1992 Patek's daughter Kimberlie was paralyzed from the neck down in a car accident. Several fund raisers were held by former teammates and the Baseball Assistance Team to help with Kimberlie's medical bills. She died on June 14, 1995.