Sam Evans is a transfer student who joins the football team in season two. Encouraged by Finn to audition for New Directions, he joins the males of the group in a performance of "Billionaire", the same song with which Overstreet studio tested for Glee.Despite some trepidation about the effect it may have on his social status, Sam eventually joins the glee club.

With the connivance of Finn and Rachel, he and Quinn are partnered for, and win, a duet competition within the group, after which their victory dinner turns into a first date; the victory later nets them a lead performance at sectionals. This becomes a relationship, but Quinn is later unfaithful to him, rekindling her romance with Finn. Sam makes a last-ditch attempt to win her back, but ends the relationship after finding out from Santana that Quinn cheated on him with Finn.

At some point after going to junior prom together, Sam and Mercedes start to secretly date. His family moves to Kentucky over the summer, but Finn and Rachel convince him to come back to New Directions late that fall in time to compete in Sectionals. Although Mercedes has a new boyfriend, he wants to get her back. In season four, he develops friendships with Blaine and Brittany, the latter of which becomes a romantic relationship.
Following Overstreet's casting, media speculation suggested Sam might have been created as a boyfriend for Kurt. Overstreet later confirmed this, but stated that his storyline had been adjusted to pair Sam with Quinn, as a result of the chemistry the producers detected between himself and Agron. Overstreet left the show when his option for being a series regular in season three was not picked up, but he returned as Sam in the eighth episode of the third season for a multi-episode arc.