Each Major League Baseball (MLB) season, one National League (NL) team wins its league's pennant, signifying that they are its champion and have the right to play in the World Series against the champion of the American League (AL). In addition to the pennant, the team that wins the NL playoffs receives the Warren C. Giles Trophy, named after Warren Giles, who was the league president from 1951 to 1969. Warren's son Bill Giles, the honorary league president and owner of the Philadelphia Phillies, presents the trophy to the NL champion at the conclusion of each NL Championship Series (NLCS). The current NL pennant winners are the Los Angeles Dodgers, who won their second consecutive NL pennant in October 2018.
For most of the history of the NL (94 years), the pennant was presented to the team with the best win–loss record at the end of the season. The first modern World Series was played in 1903, and after a hiatus in 1904, continued until 1994, when a players' strike forced the cancellation of the postseason, and resumed in 1995. In 1969, the league split into two divisions, and the teams with the best records in each division played one another in the NLCS to determine the pennant winner. The format of the NLCS was changed from a best-of-five to a best-of-seven format for the 1985 postseason. In 1995, an additional playoff series was added when MLB restructured the two divisions in each league into three. As of 2010, the winners of the Eastern, Central, and Western Divisions, as well as one wild card team, play in the NL Division Series, a best-of-five playoff to determine the opponents who will play for the pennant.
By pennants, the Los Angeles Dodgers (formerly the Brooklyn Dodgers; 23 pennants, 31 playoff appearances) and the San Francisco Giants (formerly the New York Giants; 23 pennants, 27 playoff appearances) are tied for the winningest teams in the NL. In third place is the St. Louis Cardinals (19 pennants and 28 playoff appearances), followed by the Atlanta Braves (17 pennants and 23 postseason appearances between their three home cities of Atlanta, Milwaukee, and Boston) and the Chicago Cubs (17 pennants and 20 playoff appearances as the Cubs and White Stockings). The Philadelphia Phillies were NL champions in back-to-back seasons in 2008 and 2009, becoming the first NL team to do so since the Braves in 1995 and 1996. The Dodgers were also league champions in back-to-back seasons in 2017 and 2018. Before 1903 there was no World Series as we know it today because the leagues were only loosely affiliated. As of 2018, the Giants and the Dodgers have the most World Series appearances at 20, followed by the St. Louis Cardinals with 19.
The team with the best record to win the NL pennant was the 1906 Cubs, who won 116 of 152 games during that season and finished 20 games ahead of the New York Giants. The best record by a pennant winner in the Championship Series era is 108–54, which was achieved by the Cincinnati Reds in 1975 and the New York Mets in 1986; both of these teams went on to win the World Series.
NL champions have gone on to win the World Series 48 times, most recently in 2016. Pennant winners have also won the Temple Cup and the Chronicle-Telegraph Cup, two pre-World Series league championships, although second-place teams won three of the four Temple Cup meetings. The largest margin of victory for a pennant winner, before the league split into two divisions in 1969, is 27 1⁄2 games; the Pittsburgh Pirates led the Brooklyn Superbas (now the Dodgers) by that margin on the final day of the 1902 season.
The only currently-existing NL team to have never won a pennant is the Washington Nationals (formerly the Montreal Expos). While the Milwaukee Brewers have never won a NL pennant, they did win a pennant during their time in the AL.
Single table era (1876–1968)
League Championship Series era (1969–present)
- a A mid-season labor stoppage split the season into two halves. The winner of the first half played the winner of the second half in each division in the 1981 National League Division Series. The winners played in the 1981 NLCS for the National League pennant.
- b The leagues were re-aligned in 1994 to three divisions and a wild card was added to the playoffs, but the labor stoppage cancelled the postseason. Wild cards were first used in the 1995 playoffs.
NL pennants won by franchise
- a Also known as New York Giants and New York Gothams
- b Also known as Brooklyn Dodgers, Brooklyn Robins, Brooklyn Superbas, Brooklyn Bridegrooms, Brooklyn Grooms, Brooklyn Grays and Brooklyn Atlantics. Does not include American Association pennant won in 1889
- c Also known as St. Louis Perfectos, St. Louis Browns, and St. Louis Brown Stockings. Does not include four American Association pennants won in 1885–1888
- d Also known as Milwaukee Braves, Boston Braves, Boston Bees, Boston Rustlers, Boston Doves, Boston Beaneaters and Boston Red Caps
- e Also known as Chicago Orphans, Chicago Colts and Chicago White Stockings
- f Also known as Pittsburgh Alleghenys
- g Also known as Cincinnati Redlegs and Cincinnati Red Stockings. Does not include American Association pennant won in 1882
- h Also known as Philadelphia Quakers and unofficially as Philadelphia Blue Jays
- i Also known as Houston Colt .45s Moved to the American League in 2013; won the American League pennant and World Series in 2017.
- j The Brewers were members of the American League through the 1997 season after which they switched to the National League. This table records only the Brewers' National League accomplishments. They won the American League pennant in 1982.
- k Also known as Montréal Expos. In 1994, the Expos led the National League East and had the best won-loss record in the league when the season was cut short by a labor dispute. 
- l The 19th-century Baltimore Orioles who played in the National League are no longer in existence; two current American League franchises later used the Orioles name (New York Yankees and Baltimore Orioles).