Claire Matchett is the protagonist and primary narrator of One by One. She is an elementary school teacher who is married to Noah Matchett, with whom she has a son named Aidan and a daughter named Emma. Claire met Noah in college, where she also met her best friend (and secret antagonist of the novel) Lindsay, and Noah’s roommate Jack.

Claire and Noah’s marriage began to break down after the birth of Emma, as Emma was a colicky baby and the stress took a toll on both parents, with Claire viewing Noah as unhelpful and disengaged from the family. Due to the difficulties in their marriage, Claire starts a romantic affair with Jack. She feels immense guilt about her affair, but she cannot bring herself to tell Noah the truth.

Claire is a good friend, however. She is deeply invested in Lindsay and is very upset when Warner mistreats Lindsay. She tries to speak to Lindsay about Warner, warning her about the red flags Warner displays (critiquing her body/what she eats, being overly controlling, etc.), though Lindsay does not listen. Claire also wants to stay with Lindsay’s body, even though the rest of the group wants to move on after Lindsay’s supposed death, which illustrates Claire’s devotion to Lindsay.