The first season of Gossip Girl made its official debut on CTV in Canada on September 18, 2007 at 8:00 p.m. while The CW, the original broadcast network of the show, aired the pilot a day later on Wednesday, September 19, 2007 at 9:00 p.m. eastern/8:00 p.m. central.

Serena van der Woodsen's sudden return to the Upper East Side from an unexplained exile is not welcomed by her best friend Blair Waldorf who has assumed the queen bee position in the Constance Billard junior class. Meanwhile, Blair and Nate Archibald's relationship goes sour after he admitted he had sex with Serena, which was witnessed by Chuck Bass. Meanwhile, Dan Humphrey (who goes to same school, St. Jude's, with Chuck and Nate) returns to Williamsburg, Brooklyn together with his sister Jenny who is accepted by Blair as one of her associates.

Dan asks Serena for a date after a chance encounter, only to save Jenny who was being molested by Chuck at a party hosted by Blair. Blair and Serena's relationship takes a turn for the worse when Blair reveals that Serena had a nonexistent drug disorder; in reality, it is Serena's brother Eric who tried to commit suicide and is the one inside an institution. Serena's reaction to Blair's revelation impresses Dan and decides to pursue her once more while Eric's revelation to Blair causes the reconciliation between the two best friends.

Dan's father Rufus (who was the frontman of the fictional band Lincoln Hawk) and Serena's mother Lily, who was a groupie during the 1990s, rekindle their past relationship. Serena and Dan's relationship grows fonder despite the arrival of Dan's friend Vanessa Abrams, who backs off after seeing the couple. Meanwhile, Blair and Nate's relationship takes a bad turn when Blair finds out Nate still has feelings for Serena. This eventually caused her to break up with him and pursue a secret relationship with Chuck. Nate tried to get back to Blair, with his parents' prodding to help them in their business deal with the Waldorfs but in the end remains steadfast in ending their relationship.

Jenny, while being used by Blair, drags her mother Alison back to Brooklyn to make her parents patch up their differences, while Rufus and Lily's relationship is kept under wraps. Blair finally breaks up with Chuck when he caused a scene at the debutante ball. This causes Blair and Nate to hook up again, but with Chuck blackmailing her, she then avoids Nate. Meanwhile, Lily accepts Chuck's father Bart's marriage proposal, which causes her to end her relationship with Rufus, with persuasion from Serena who'd rather have Chuck as her stepbrother than Dan.Alison and Rufus fail to patch up their differences and Alison leaves for the Hudson after Christmas.

Seeking to end the blackmailing, Blair orders Chuck to stop but this causes him to reveal her affairs with two men to Gossip Girl. Nate refuses to believe it but after Jenny overheard Dan and Serena talking about it, she tells Nate what she heard, causing Nate to break up with Blair. It also causes Blair to lose her queen bee position and she almost flees for France, if not for Serena urging her to stay. After spring break, Blair battles Jenny for the queen bee position, with Blair ultimately winning after she exposed Jenny's boyfriend Asher as a homosexual, but not before having Eric's permission, who was the one seen making out with Asher.

Serena then has to deal with the arrival of her friend Georgina Sparks who is determined to expose Serena's big secret - that she caused someone to die. Not wanting Dan to know anything about this, she lied about sleeping with someone else, which causes Dan to promptly break up with her. After telling Blair, Nate and Chuck what happened and talking to the dead person's parents, Serena felt relieved and is ready to confront Georgina when she finds out that Georgina, taking the pseudonym Sarah, has swept Dan off his feet, and is trying to sleep with him because she wants to hurt Serena.

Meanwhile, Nate informs Blair of his relationship with Vanessa, and Rufus and Lily made out after a Lincoln Hawk concert, reigniting their relationship a day before her wedding with Bart. Dan finds out "Sarah" is really Georgina, prompting Georgina to come up with a clever lie to mask the truth about her past. "Sarah" uses this lie to make herself seem vulnerable to Dan. This partially works in the sense that Georgina spends the night with Dan (in which Serena catches her coming out of his bedroom in the morning), however Dan later confirms that he and Georgina did not sleep together. Serena tells Dan the truth about everything, and he calls upon the help of Blair so they can destroy Georgina for good. They call her parents in, giving them the idea to send her to boot camp, and Georgina is presumably gone from the show.

It is revealed that Rufus and Lily had sex the night before her wedding, prompting her to have to make a decision between him and Chuck's father. Rufus suprises Lily in the brides chamber and offers to call off the wedding. Lily tells Rufus she loves him and then walks down the isle to marry Bart. Her heart doesn't really seem to be in it though and Rufus seems sad so there are questions of if they really will end their relationship for good.

Because of "Sarah", Serena confronts her own feelings and decides that she doesn't care if Dan did sleep with Georgina, she still wanted to give their relationship a try, however Dan cannot get over Serena's lies and ultimately decides to break up with her. Meanwhile, Nate's dad is better after going to rehab and is thought to win his court case, unfortunately, Chuck catches Nate's father doing a deal and tells Nate who then confronts his father, only to find out that while his father is sober, it is unlikely he will win in court and so bought a fake passport to leave the country and the US government's sentence. Chuck shows loyalty to Nate by telling him about his father, which ultimately rekindles their friendship. Chuck continues his "rekindling" streak by confessing how he really feels to Blair prompting them to get back together.

The finale showed segments of the summer which implied that Chuck and Blair are still going strong and are planning to vacation in Tuscany for the summer but things don't go according to plan. Chuck's father tells him he would be a changed man by the time summer ends, but are interrupted after Lily introduces her interior decorator Amelia (played by Lydia Hearst). After a fear of no longer being a single man, Chuck throws out the flower bouquet he bought for Blair, taking out a single rose and giving it to Amelia. Meanwhile, Blair who is waiting at the airport meets a man who is to board a plane and the two introduce each other. Soon she receives a text from Chuck and realizes that he isn't going to make it and boards the plane with the mysterious man. Toward the ending, scenes are shown having Nate and Serena hanging out, as were Vanessa and Dan. Season 1 ends with episode eighteen, "Much I Do About Nothing."