The 2012 National League Championship Series was a best-of-seven playoff in Major League Baseball’s 2012 postseason pitting the third-seeded San Francisco Giants against the defending World Series champion and fifth-seeded St. Louis Cardinals for the National League pennant and the right to play in the 2012 World Series. The series, the 43rd NLCS in league history, began Sunday, October 14, and ended Monday, October 22, with Fox airing all games in the United States. In shades of the 1996 NLCS, a series where the Cardinals blew a 3–1 series lead where they were outscored 32–1 over the final three games, the Giants came back from a 3–1 deficit and outscored the Cardinals, 20–1, over the final three games to win the series, 4–3.

This was the third postseason meeting between the Giants and the Cardinals and also marked the first time in MLB history since the creation of the League Championship Series in 1969 that the last two World Series champions faced off against each other for the pennant. The Giants won in 2010 while the Cardinals won in 2011. Coincidentally, the previous two postseason meetings between the two teams occurred in the NLCS, which both ended on October 14 (the day of 2012's Game 1): the Cardinals won Game 7 of the 1987 NLCS, and the Giants triumphed in the pennant-clinching Game 5 of the 2002 NLCS.

The Giants would go on to sweep the Detroit Tigers in the World Series in four games.

San Francisco won the series, 4–3.

The Cardinals scored first in the second inning, with a Yadier Molina single followed by a two-run home run by David Freese. In the fourth inning, Daniel Descalso doubled and scored on a Pete Kozma double; Kozma then stole third base during Lance Lynn's at-bat and scored on a Jon Jay single. With Jay on first, Carlos Beltrán hit a two-run home run to give the Cardinals a 6–0 lead; Giants starting pitcher Madison Bumgarner was then replaced by George Kontos, who got Matt Holliday to pop out to end the inning.

The Giants rallied back against Cardinals starting pitcher Lance Lynn in the bottom half of the fourth inning. Lynn gave up a leadoff single to Marco Scutaro, who later advanced to third on a Hunter Pence single and scored on a Brandon Belt single that also advanced Pence to third. Gregor Blanco then tripled to score Pence and Belt, and Brandon Crawford doubled to score Blanco, which cut the Cardinals' lead to 6–4. Lynn was then replaced by Joe Kelly, who got Ángel Pagán to ground into a force play to end the inning.

Neither team's bullpen allowed a run for the rest of the game; additionally, the Giants' bullpen did not allow a runner into scoring position over 5+1⁄3 innings, while the Cardinals' bullpen only allowed one runner to advance into scoring position over the same number of innings. Cardinals reliever Edward Mujica earned the win.

Cardinals starter Chris Carpenter gave up a home run to the leadoff hitter Ángel Pagán to give the Giants an early one-run lead. The lead was short-lived, however, as Carpenter hit a double in the top of the second inning that scored Pete Kozma, who walked with two outs. The game remained tied until the bottom of the fourth inning, when the Giants scored four runs, three of which were unearned amid two Cardinals errors. Brandon Belt hit a double off Carpenter and advanced to third on Gregor Blanco's single. Brandon Crawford then reached first base on a throwing error by first baseman Allen Craig; Belt scored on the play and Blanco advanced to second. Crawford and Blanco then advanced to second and third, respectively, on Vogelsong's sacrifice bunt, and Pagán was walked to load the bases. Marco Scutaro—who had been involved in a collision with Cardinals left fielder Matt Holliday in the first inning in what some termed a "questionable" slide into second base—then hit a single to left field that went between Holliday's legs, allowing Blanco, Crawford, and Pagán to score.