At the 2007 French Open, he made the second round of the men's doubles tournament with Feliciano López before they lost in three close sets to the number 4 seeds Fabrice Santoro and Nenad Zimonjić, who won 7–5, 1–6, 6–4.

[4] He reached the quarterfinals of the 2008 Abierto Mexicano Telcel in Acapulco, Mexico, an International Series Gold tournament, before losing to José Acasuso 7–6, 6–3.

In 2009, Granollers won three ATP doubles titles at the 2009 Brasil Open, the 2009 Copa Telmex, and the 2009 Kremlin Cup, teaming up with Tommy Robredo, Alberto Martín, and Pablo Cuevas respectively.

[10] In November, Granollers claimed the title at the Valencia Open by defeating Juan Mónaco in three sets and said, "Winning here has been the biggest achievement in my whole career.

"[11] He beat four Top 20 players: Alexandr Dolgopolov, Marin Čilić, Gaël Monfils and Juan Martín del Potro en route to the final at the ATP World Tour 500 tournament.

[11] Granollers played for the victorious Spain Davis Cup team in 2011, losing the doubles rubber (with Fernando Verdasco) in the quarterfinal against United States.

[12] Marcel Granollers reached the fourth round of a Grand Slam for the first time at French Open, losing to David Ferrer in three straight sets.

He made it also to the fourth round of the US Open in singles for the first time, where he lost to top-seed Novak Djokovic in straight sets.

Granollers suffered a significant loss in form, with only one tour-level late round appearance: the semifinals in Zagreb Indoors losing to Andreas Seppi.

He reached the quarterfinals of the 2016 Monte-Carlo Rolex Masters before losing to Gaël Monfils in straight sets, making the main draw as a lucky loser.

With his new partner Horacio Zeballos, Granollers won 6 titles starting in August 2019, and also made his first Grand Slam doubles final at the 2019 US Open, losing to the World No.

[23] Granollers with Zeballos reached his second ATP Finals championship match but lost to Joe Salisbury and Rajeev Ram.

At the 2024 BNP Paribas Open in Indian Wells, Granollers and Zeballos reached the final, saving a match point.

At the 2024 French Open, they reached their third consecutive semifinal at this Major defeating 15th seeds Hugo Nys and Jan Zieliński, and then Tomas Machac and Zhang Zhizhen.

His comparatively technically weak groundstrokes are underpowered with low takebacks on both wings but they provide a decent defensive framework.

[32] He is also known for his heavy grunting, so much as to result in ridicule and accusations of gamesmanship due to its loud volume and questionable timing during matches.