Winning 300 games is a feat that is much more difficult to achieve now compared to the past due to the increased use of relief pitching, which has reduced the number of decisions for starting pitchers. In addition, Maddux has pitched his entire career in the era of the 5-man rotation, in which starters are given fewer starts per season. For that reason, some baseball historians have said he may be the last pitcher to achieve 300 career wins for decades, if not ever. Amazingly, on July 26, 2005, Maddux joined an even more exclusive club when he recorded his 3,000th strikeout, a feat generally accomplished by power pitchers, not a finesse pitcher like Maddux. Although this feat has been accomplished by several other pitchers, Maddux is one of just two who have done so while allowing fewer than 1,000 walks. The only other pitcher who allowed so few walks with as many strikeouts is former fellow Cub Fergie Jenkins. Maddux has won 20 games only twice, in 1992 and 1993 (although interrupted seasons in 1994 and 1995, when Maddux won 16 and 19 games respectively, likely cost him more). Maddux has won 19 games five times, and 18 games twice!

Maddux was drafted in the second round of the 1984 amateur draft by the Cubs, making his Major League debut in September 1986 after some time in the minor leagues. At the time, he was the youngest player in the majors. After spending seven seasons in Chicago, Maddux signed with the Atlanta Braves in 1993 as a free agent, and starred for the team through 2003. In his time with the Braves, he pitched in three World Series, his team winning one in 1995. He returned to the Cubs as a free agent prior to the 2004 season. He was the first Major Leaguer to earn over $100,000,000 in salary in a career.

During his brief 1986 call-up, Maddux defeated his older brother, Philadelphia Phillies pitcher Mike Maddux, marking the first time rookie brothers had ever pitched against each other. In 1987, his first full season in the Majors, Maddux finished with a disappointing 6-14 record and 5.61 ERA. In 1988, Maddux surprised the league by finishing 18-8 with a 3.18 ERA. This began a streak of 17 straight seasons in which Maddux recorded 15 or more wins. No other pitcher has achieved a streak as long as Maddux's. Cy Young ranks second with 15 straight 15-win seasons.

Maddux established himself as the Cubs' ace in 1989, winning 19 games, including a September game at Montreal's Olympic Stadium that clinched the Cubs' second National League Eastern Division championship. Manager Don Zimmer tabbed him to start Game 1 of the National League Championship Series against the San Francisco Giants. It was a rough postseason debut for Maddux, as he was chased in the fourth inning, the lethal blow being Will Clark's grand slam home run with 2 outs in the fourth.

After strong 1990 and 1991 seasons, Maddux came into his own in 1992, winning 20 games and his first National League Cy Young Award. During the 1992 season, negotiations between him and the Cubs became contentious and eventually broke off. Cubs' general manager Larry Himes claimed that Maddux and his agent, Scott Boras, made unreasonable demands, but Maddux and Boras insist that Himes and Tribune Company executive Jim Dowdle failed to work in good faith with them.

After the 1992 season, Maddux filed for free agency and the Cubs decided to pursue other free agents, including Jose Guzman, Dan Plesac and Candy Maldonado. Maddux signed with Atlanta, and he made his Braves' debut as Opening Day Starter against the Cubs at Wrigley Field. Maddux beat his old teammates 1-0, the losing pitcher being Maddux's good friend Mike Morgan.

Maddux's tenure with the Braves allowed him to pitch alongside Tom Glavine and John Smoltz. The three of them formed the core of some of the best pitching staffs in the history of the game, and were a large measure of the reason for the Braves winning 10 straight division titles during Maddux's Braves tenure (1993-2003, with the strike year of 1994 being excluded).

Maddux has pitched in 11 Division Series contests, 15 League Championship games and five World Series games, and has a 3.22 ERA in 190.0 post-season innings.

Maddux is also known as the best-fielding active pitcher in the game, having earned 15 Gold Glove Awards, one shy of the major-league record of 16 shared by Jim Kaat and Brooks Robinson. Maddux won 13 straight Gold Gloves from 1990 to 2003.

Maddux is also an eight-time National League All-Star selection.

Maddux is a right-handed pitcher known for his pinpoint accuracy and his ability to psyche out hitters. While the speed of his pitches have decreased with time, and never truly having had a blazing fastball like such contemporaries as Roger Clemens and Randy Johnson, Maddux relies on location rather than power, although he is capable of hitting the low nineties every once in a while. Baseball Hall of Famer Wade Boggs said of Maddux, "It seems like he's inside your mind with you. When he knows you're not going to swing, he throws a straight one. He sees into the future. It's like he has a crystal ball hidden inside his glove." Dwight Gooden once commended Maddux, saying, "You wish there was another league he could get called up to." Joe Morgan once said that "Greg Maddux could put a baseball through a Life Saver." Maddux was also remarkable for the late movement on his pitches, which, combined with his superb command, made him one of the most effective groundball pitchers in history; hitters were often unable to make solid contact with his pitches.

Maddux's best season was likely in 1995 when he finished 19-2 with an incredible 1.63 ERA in a year when the overall National League ERA was 4.23. In the strike-shortened 1994 season, he had an even lower ERA of 1.56, the best single-season ERA among currently active pitchers, which compared even more favorably to the NL in that year (4.26), but had a 16-6 record. He finished with a 2.20 ERA in 1997 and would have likely won the Cy Young Award that season had Pedro Martinez not had an even more spectacular season. In 1998, Maddux carried a cumulative 1.65 ERA through late August, but a late-season slump caused his ERA to rise to 2.22. He still ended up with the lowest ERA in the National League, struck out over 200 batters for the only time in his career, and won 18 games but was overlooked by the voters in the Cy Young balloting.

Maddux has never walked more than 82 batters in any season of his career. He has averaged fewer than 2 walks per game. In 1997, Maddux allowed 20 walks in 232+ innings, or 0.77 per 9 innings. Another strength is his defense, and he is known for his ability to field his position well. On November 14, 2002, he won his 13th straight Gold Glove Award, and added a 14th award in 2004, and a 15th in 2005.

Maddux also won four straight Cy Young Awards from 1992 to 1995, a feat matched only by Randy Johnson. He has finished as high as third in MVP voting, and has been in the top ten several times.

On April 28th, 2006, Maddux began his 21st season, and final under contract with the Chicago Cubs, by winning each of his first five starts. This marked the third time winning five games in a month for Maddux, and the first time in his career that he had ever started a season off 5-0.

On August 7, 2004, Maddux defeated the San Francisco Giants, 8-4, to garner his 300th career victory. He has 325 career wins under his belt, surpassing pitching greats Nolan Ryan and Don Sutton by one win. On July 26, 2005, Maddux struck out Omar Vizquel to become the thirteenth member of the 3000 strikeout club and only the ninth pitcher with both 300 wins and 3,000 strikeouts. He is also one of only two pitchers with 3,000 strikeouts and fewer than 1,000 walks.

In 2003, he earned a salary of $14,750,000. His contract with the Cubs will pay him $8 million in 2004 and includes $8 million per year clauses that automatically go into effect for 2005 and 2006 if he pitches 200 or more innings in those years.

Maddux, whose nicknames include "The Mad Dog" and "The Professor," is an avid golfer.

He graduated from Valley High School in Las Vegas, Nevada and currently maintains his residence there.

During the construction of the Olympic Stadium in Atlanta, which was converted into Turner Field after the 1996 Summer Olympics, the Braves front office challenged the golden trio of Braves starters (Maddux, Glavine, and Smoltz) to win the World Series in 1995 by saying that if they did, a putting green would be installed in the locker room at Turner Field.

A baseball traditionalist, Maddux insists that the Cubs wear their white home jersey on the days that he is their starting pitcher. He also prefers to be called a baseball player, not merely a pitcher; he is a perennial Gold Glove winner and has a reputation as an effective situational batter.