Smoltz made his Major League debut on June 23, 1988. He posted poor statistics in a dozen starts, but in 1989, Smoltz blossomed. In 29 starts, he recorded a 12–11 record and 2.94 ERA while pitching 208 innings and making the All-Star team. Teammate Tom Glavine also had his first good year in 1989, raising optimism about the future of Atlanta's pitching staff. Smoltz began the 1991 season with a 2–11 record. He began seeing a sports psychologist, after which he closed out the season on a 12–2 pace, helping the Braves win a tight NL West race. His winning ways continued into the 1991 National League Championship Series. Smoltz won both his starts against the Pittsburgh Pirates, capped by a complete game shutout in the seventh game, propelling the Braves to their first World Series since moving to Atlanta in 1966. Smoltz had two no-decisions against the Minnesota Twins, with a 1.26 ERA. In the seventh and deciding game, he faced his former Detroit Tiger hero, Jack Morris. Both starters pitched shutout ball for seven innings, before Smoltz was removed from the 0–0 game during a Twins threat in the eighth. Atlanta reliever Mike Stanton pitched out of the jam, getting Smoltz off the hook, but Morris would eventually pitch a 10-inning complete game victory. The next year, Smoltz won fifteen regular season games and was the MVP of the 1992 National League Championship Series, winning two games. He left the seventh game trailing, but ended up with a no-decision as the Braves mounted a dramatic ninth-inning comeback win. In the World Series that year, Smoltz started two of the six games in the series, with a no-decision in Game Two and a win with the Braves facing elimination in Game 5. Before the 1993 season, the Braves signed renowned control pitcher Greg Maddux, completing what many consider to be the most accomplished starting trio ever assembled on a single Major League team. Smoltz again won fifteen games, but suffered his first postseason loss to the Philadelphia Phillies in the NLCS despite a 0.00 ERA. Smoltz had a 6-10 record in the strike-shortened 1994 season, and during the break, had bone chips removed from his elbow. Returning as the Braves' #3 starter, he posted a 12–7 record in 1995. Smoltz had shaky postseason numbers, avoiding a decision despite a 6.60 ERA. But Smoltz and the Braves won the franchise's only World Series in Atlanta, thanks in great part to Maddux and Glavine, who had begun to overshadow Smoltz. The following season, 1996, was the best of Smoltz's career. He went 24–8 with a 2.94 ERA and 276 strikeouts, including winning a franchise record fourteen straight decisions. He won the National League Cy Young with 26 of the 28 first-place votes. Smoltz's effectiveness in 1997 was only slightly less than his Cy Young season, but frugal run support limited him to a 15–12 record. Smoltz was also awarded a Silver Slugger Award for his batting.
Video from John Smoltz
Smoltz continued to post excellent statistics in 1998 and 1999, but he was spending significant time on the disabled list and missed about a fourth of his starts. In 1999, Smoltz began experimenting with both a knuckleball and a three-quarters delivery, though he rarely used either in game situations. He underwent Tommy John surgery prior to the 2000 season, missing the entire year. When he was unable to perform effectively as a starter in 2001, Smoltz made a transition to the bullpen, filling a void as Atlanta's new closer down the stretch, replacing John Rocker. In 2002, his first full season as a closer, Smoltz broke the National League saves record with 55 saves (the previous record was 53; Éric Gagné would equal Smoltz's new record a year later). Smoltz finished third in the Cy Young Award voting. Injuries limited Smoltz slightly in 2003, but he still recorded 45 saves with a 1.12 ERA in 64.3 innings pitched. In 2004, Smoltz finished with 44 saves, but was frustrated with his inability to make an impact as a closer during another Braves' postseason loss. By this point, Smoltz was all that remained of the once-dominant Atlanta Braves' rotation of the 1990s. Tom Glavine had moved on to play for the New York Mets, a divisional rival, while Greg Maddux returned to his old team, the Chicago Cubs.
After three years as one of baseball's most dominating closers, the team's management agreed to return Smoltz to the starting rotation prior to the 2005 season. Smoltz's renewed career as a starter began inauspiciously. He allowed six earned runs in only 1 2/3 innings—matching the shortest starts of his career—as the Braves were blown out on Opening Day by the Florida Marlins. Poor run support contributed to an 0–3 start despite stronger pitching performances by Smoltz. After these initial difficulties, though, things fell into place. At the All-Star break, Smoltz was 9–5 with an ERA of 2.68 and was chosen for the 2005 NL All-Star team. Smoltz gave up a solo home run to Miguel Tejada in the second inning of the American League's 7–5 victory and received the loss. For his career, he is 1–2 in All-Star games, putting him in a tie for the most losses. Smoltz finished 2005 at 14–7, with a 3.06 ERA with 169 strikeouts while allowing less than one hit per inning. Smoltz had answered the critics who doubted he would be able to reach the 200 inning plateau after three years in the bullpen. Nonetheless, Smoltz's increased workload caused him to wear down towards the end of the season. Despite a sore shoulder, Smoltz pitched seven innings in the Braves' 7–1 win over the Houston Astros in Game Two of the 2005 NLDS. It was the only game the Braves would manage to win in the series against the eventual National League champions. The victory over Houston gave Smoltz a 13–4 record as a starter (15–4 overall) with a 2.65 ERA in the postseason. He has the second most postseason wins behind only Andy Pettitte with 19. They are followed by Tom Glavine, and Greg Maddux. In 2006, Smoltz finished the season with a record of 16–9, an earned run average of 3.49, and 211 strikeouts. He was tied for the National League lead in wins, and was third in strikeouts. The fact that the Braves bullpen blew six of Smoltz's leads in 2006 robbed him of a strong chance at a 20-win season. On September 21, 2006, the Braves announced they had picked up Smoltz's $8 million contract option for the 2007 season. On April 26, 2007 Smoltz agreed to a contract extension with the Braves. The extension includes a $14 million salary for the 2008 season, a $12 million vesting option for 2009 dependent on Smoltz's ability to pitch 200 innings in 2008, and a $12 or $13 million team option for 2010 dependent on Smoltz's ability to pitch 200 innings in 2009.
2007 was a year of reunions and milestones for Smoltz. On May 9, he faced Greg Maddux for the first time since July 10, 1992. Smoltz earned a win in a 3–2 victory over the San Diego Padres; Maddux received a no-decision. On May 24, exactly eleven years to the day after recording his 100th win, Smoltz recorded his 200th win against Tom Glavine. He faced Glavine 3 other times faring 3–1 overall against him. On June 27, Smoltz, Glavine and Maddux all recorded wins on the same day. On August 19, 2007, Smoltz set the new Atlanta Braves strikeout record by striking out Arizona Diamondbacks' Mark Reynolds. It was his 2,913th strikeout and he passed Phil Niekro on the Braves all-time list; striking out a season-high 12 in the game. He finished the year 14–8 with a 3.11 ERA and 197 strikeouts. The stalwart pitcher was the only holdover on the Braves' roster from their 1991 worst-to-first season until Glavine returned to the Braves after an absence of several years following the 2007 season. On April 22, 2008, Smoltz became the 16th pitcher in Major League Baseball history to reach 3,000 career strikeouts. He is one of four pitchers to strike out 3,000 batters for one team, joining Walter Johnson, Bob Gibson and Steve Carlton. On April 28, 2008, Smoltz was placed on the 15 day disabled list due to an inflamed right shoulder. On May 1, 2008, Smoltz indicated that he intended to return to being a relief pitcher. After coming off the disabled list on June 2, 2008, he blew his first save opportunity in three years. Two days later, the Braves placed him back on the disabled list. John Smoltz underwent season-ending shoulder surgery on June 10, 2008. His contract expired at the end of the season, and the contract offer from the Braves was not sufficient to keep him.
In December 2008, several members of the Boston Red Sox organization including pitching coach John Farrell, Vice President of Player Personnel Ben Cherington, and assistant trainer Mike Reinold, flew to Atlanta, Georgia to participate in a 90-minute workout with Smoltz. Throwing for only the second time since having surgery on a torn labrum in his pitching shoulder, Smoltz threw a 50-pitch side session and showcased not only his tremendous progress since the surgery, but an arsenal of well-developed pitches which has made him so successful throughout his career. Smoltz impressed the Red Sox members enough during the workout that less than a month later, a one-year contract was offered by the organization. On January 13, 2009, Smoltz signed a one-year contract with the Boston Red Sox for a reported base salary of $5.5 million with roster time incentives and miscellaneous award incentives which could net as much as $10 million. He made his first start in the Boston Red Sox rotation June 25, 2009, allowing seven hits and five runs through five innings. Smoltz struggled his entire time with the Red Sox posting a 2-5 record over eight games with an 8.32 ERA and no quality starts. He was designated for assignment on August 7, 2009, after a 13-6 loss to the Yankees, giving the Red Sox 10 days to release, trade, or send him to the minors. The Red Sox offered Smoltz a minor league stint in order to prepare him to be placed in the bullpen, but he rejected the offer, leaving the Red Sox the options of either releasing or trading him. On August 17, 2009 the Red Sox released Smoltz. On August 19, 2009, Smoltz signed with the St. Louis Cardinals. Smoltz made his debut against the San Diego Padres on August 23, 2009. In his first game for the Cardinals, Smoltz went five innings, striking out nine and walking none, while setting a Cardinals franchise record by striking out seven batters in a row. That win against the Padres with the Cardinals was his only win with them that season. Smoltz finished 1-3 with an ERA of 4.26 with the Cardinals. He was 3-8 with an ERA of 6.35 overall with the Red Sox and Cardinals. In Game 3 of the 2009 NLDS, Smoltz finished with a 4.50 ERA after pitching 2 full innings, giving up 4 hits.