Phil and his brother Joe Niekro amassed 539 wins between them, the most combined wins by brothers in baseball history. Phil Niekro's 121 career victories after the age of 40 is a major league record, and his longevity is attributed to the knuckleball, which, while a difficult pitch for pitchers to master, is easy on the arm and often baffles hitters due to its fluttering trajectory. He is also the uncle of former first baseman and pitcherLance Niekro. The baseball field in Phil's hometown of Bridgeport, Ohio has been named Niekro Diamond in honor of Phil and Joe Niekro.
Niekro was the last MLB pitcher to have both won and lost 20 or more games in the same season; with the 1979 Braves, Niekro finished with 21 wins and 20 losses. His third and final 20-win season came in 1979; it was also the second and final year that he lost 20 games.
Niekro was signed to the Braves by scout Bill Maughn in 1959 for $250. His pitching featured the knuckleball, which frustrated major league hitters. Ralph Kiner compared Niekro's special pitch to "watching Mario Andretti park a car."Pete Rose said, "I work for three weeks to get my swing down pat and Phil messes it up in one night... Trying to hit that thing is a miserable way to make a living." Catcher Bob Uecker was also frustrated by the pitch at times, saying, "Niekro struck out a hitter once and I never touched the ball. It hit me in the shinguard, bounced out to Clete Boyer at third base and he threw out the runner at first. Talk about a weird assist: 2-5-3 on a strikeout."
He was popular in the city of Atlanta for remaining loyal to a team that often had a losing record, as well as for his contributions to Atlanta charities. On August 5, 1973, Niekro threw a no-hitter against the San Diego Padres. The no-hitter was the first for the Braves after moving to Atlanta. He was often the only star on the Braves teams. In 1979, for example, Niekro tied his brother for the league lead with 21 wins while playing for a team that only won 66.
Niekro pitched for 20 seasons for the Braves (two of those seasons when the team was still in Milwaukee). During his tenure in Atlanta, Niekro was selected for five All-Star Teams, won five gold gloves, led the league in victories twice and earned run average once. Niekro was also a key to the only two division titles Atlanta won before 1991. In 1969, he had a 23–13 season with a 2.56 ERA and finished second in Cy Young balloting to New York Mets sensation Tom Seaver. In the final days of the season, Niekro started three of seven games, going 3-0 as the Braves won the division. He lost his only appearance in the NLCS, as Atlanta was swept by the Mets.
In 1982, at the age of 43, Niekro led the Braves' pitching staff with a 17–4 season. On October 1, with the Braves clinging to a one-game lead over the Los Angeles Dodgers, Niekro beat the San Diego Padres almost single-handedly by throwing a complete game shutout and hitting a two run home run. Niekro started Game One of the subsequent NLCS against the St. Louis Cardinals and pitched well, but the game was called on account of rain just before it became official. He pitched six innings of Game Two and left with a 3–2 lead. However, the Cardinals scored 2 late runs after Niekro left the game and would eventually sweep the series.
The Braves released Niekro after the 1983 season and he signed with the New York Yankees and went on to win 16 games and make the last of his five All-Star appearances. It was while pitching for the Yankees that Niekro gained entry into the 300 win club with a shutout win over the Toronto Blue Jays on October 6, 1985. At 46 years, 188 days, Niekro became the oldest pitcher to pitch a shutout in the major leagues; this record stood for nearly 25 years before Jamie Moyer (47 years, 170 days) bested the feat in May 2010; for Niekro, this complete-game shutout would be his 300th win. He did not throw his trademark knuckleball until the final hitter, former AL MVPJeff Burroughs. Prior to facing Burroughs, Niekro's teammate and brother Joe visited the mound in the role of "substitute pitching coach" and jokingly suggested that an intentional walk was in order. Instead, Niekro struck Burroughs out to end the game.
After two seasons in New York, Niekro pitched for the Cleveland Indians and Toronto Blue Jays in 1986 and 1987. The Blue Jays released him after he pitched ineffectively, and the Braves brought him back for one last start to wrap up his career late in the 1987 season. At the age of 48, Niekro was the oldest player in major league history to play regularly until Julio Franco, and his 24 seasons in the major leagues without a World Series appearance is a major league record. His total of 5,404⅓ innings pitched is the most by any pitcher in the post-1920 live-ball era. He only appeared in the postseason twice, making a playoff start in 1969 and again in 1982, both for Braves teams that lost the series.
After the end of his professional baseball career, Niekro managed the all-women Colorado Silver Bullets baseball team. He was elected to the Hall of Fame in 1997. Niekro tutored his nephew, Lance Niekro, to throw a knuckleball after Lance's unsuccessful stints as a power-hitting first base prospect with the San Francisco Giants.
Niekro is a member of the Kiz Toys Board of Advisors. Kiz Toys is a toy company based out of Cumming, Georgia, and Niekro advises the company on the KizSport baseball line, reviewing product designs and development on an ongoing basis and offering suggestions on current and future products.
The Gwinnett Braves' stadium has a restaurant named Niekros after him; it features the Knucksie Sandwich made of barbecue and cole slaw atop a corn muffin, said to be his favorite.