With the acquisition of star players Kevin Garnett and Ray Allen via trade from the Minnesota Timberwolves and Seattle SuperSonics respectively, Paul Pierce finally had a pair of superstar teammates to work with. But with the unknown of having three great players coexisting, plus the players that were given up just to get Garnett, a successful season in 2007–08 was not a sure thing. Nevertheless, the Celtics started the season hot, winning their first eight games, and going into 2008 with a 26–3 record. They finished the season with a 66–16 record—the most wins in a single season since the last time they won the NBA Finals, in 1985–86. Their record guaranteed them home court advantage for the entire playoffs.

The 2008 NBA Playoffs, however, were bumpier than many believed they should be. Their First Round series was against the eighth-seeded Atlanta Hawks. At home, the Celtics were dominant: their lowest home margin of victory against the Hawks in the playoffs was 19, in Game 2. However, the Hawks were able to beat the Celtics in Atlanta. The series went seven games, with the home team winning each game.

The Second Round was against LeBron James and the Cleveland Cavaliers. Once again the series went to seven games, with the home team winning each one.

In the Eastern Conference Finals, the Celtics faced Chauncey Billups, Richard Hamilton and the Detroit Pistons. In Game 2, the Celtics finally lost at home, and rumors began to fly that the Celtics had gotten too tired from consecutive seven-game series to pull off a title, especially with the Pistons having taken their first two series in six and five games, respectively. But the Celtics bounced back to win Game 3 on the road in Detroit. The series continued, and the Celtics took down the Pistons in six games, winning the deciding game on the road.

The 2008 NBA Finals were contested with Kobe Bryant, Pau Gasol and a Los Angeles Lakers team in the middle of a dominant playoff run. They swept the Denver Nuggets in the first round, took the Utah Jazz in the second round in six games, and extinguished the repeat hopes of the defending-champion San Antonio Spurs in five games in the Western Conference Finals.

The first few games of the series started with the Celtics once again dominating at the TD Banknorth Garden, the Celtics home turf. Game 1 saw Paul Pierce come back after apparently suffering a knee injury earlier in the game, and taking over the game for a 98–88 Celtics win. But in Game 2, Boston nearly lost a 24-point lead, ultimately winning, 108–102. Squandered leads would later become the story of the series. When the Lakers returned to Staples Center and won Game 3, 87–81, then took a 24-point lead in the second quarter of Game 4, some believed momentum in the series had shifted the Lakers' way.

However, the Celtics did not give up. Led by a bench that outscored the Lakers bench by 20 points, they fought back. The Celtics locked up their defense and took over Game 4 with a crushing 97–91 victory, the biggest comeback in NBA Finals history. Although the Lakers took Game 5, 103–98, the series went back to Boston for Game 6, and the Celtics finished it off with a dominating 131–92 victory. The "Boston Three Party", as Garnett, Allen and NBA Finals MVP Paul Pierce became known, had finally brought a 17th banner to Boston, the first new banner for the new Garden and the first such win in 22 years.