James is shallow, driven, sometimes an airhead, and, like Logan, sometimes panics under pressure, but is a good friend and looks out for his band mates. Of his band mates, he is closest to Carlos, whom he loves to play video games and goof around with. He is described as solid-voiced and driven beyond belief.
James Diamond is firstintroduced as the pretty boy who only wants to be famous and desperately wants to get out of Minnesota to be a pop star in California. He is currently 18 years old (15 to 16 in Season 1, 16 to 17 in Season 1, while turning 18 in Big Time Movie).
He takes the opportunity of Gustavo Rocqué coming to town to do so. Once he gets there, he switches numbers with Logan. Then Logan goes and does it, then he switches numbers with Carlos, then Carlos does it, and finally switches with Kendall, who doesn't let him switch, assures him that stardom is his destiny and he goes in. Gustavo told him that he has no talent, so then Kendall sings The Giant Turd Song. Then, the security guards come because he pushed Gustavo over, so he joins Kendall, Carlos, and Logan in the brawl with the security guards. He goes to Hollywood, California with the others and instantly is in love with the city and the girls. James' favorite shirt is his lucky white v-neck, which gets ruined while the boys started squirting each other with fruit water in the recording booth in Big Time Audition.
When the boys are getting ready for their first concert, they try hard. It's their someday and James has been waiting for this in a long time. But then Arthur Griffin says that the boy band is dead and they get sent home. James isn't too happy about it, and signs with Hawk Records, but he soon finds out that Hawk does things a little differently. Then he goes back to Big Time Rush, and tries and do their first concert, but the problem is that Hawk kidnaps them, and they are trying to get back to the concert before the people leave.
In Big Time Love Song, James gets a crush on Jo. He is constantly spraying himself with Cuda, which he had an allergic reaction to. He was sneezing constantly and Kelly Wainwright took him to the hospital. He later tries to flirt with Jo, only to realize (thanks to Camille) that the Cuda had been recalled due to high allergic reactions. So then he gets the shot and sings Any Kind of Guy with the boys.
In Big Time Jobs, the boys are trying to pay Gustavo back, so James tries to get a job as a model/actor. He has Katie be his talent manager and eventually gets a job as an elbow model after being attacked with "handsome." Soon, he finds out that Katie said that Gustavo was paying for everything. So then Gustavo breaks a window, and the boys, Gustavo, and Kelly have to pay Griffin back by doing a car wash.
During the events of Big Time Dance, James is shown to be very popular with the girls. Logan comes up to him and asks if he could help him with asking out Camile (because Logan has never asked a girl out), so while trying to help Logan ask out Camille, he accidentally asks out multiple girls who all say yes. This eventually gets out of hand and all the girls go after him.
James loves wearing bandannas and pushes the group to wear them as well, although they refuse. His obsession with bandannas is so strong that he has a superhero alter-ego called "Bandanna Man". He can somehow spin around until he turns into Bandana Man or he can just tie bandanas all around him. According to Carlos, he always gets the girls and declares himself the "pretty one". Though quite self-absorbed most of the time, he is capable of caring for people. This is evident in the episode "Big Time Break", where he rejects an acting career in order to cheer Camille up.
Also in Big Time Audition, he said that he's going to marry Nicole Scherzinger from Pussycat Dolls and he's going to do that by being famous, sing at the sold out arena, have 5 houses, and make the girls go crazy over him. In the same episode, when he got fired by Gustavo, he said that he could be a model because he still good looking, or he's going to be a star in a reality show.
In Big Time Break, he wants to be an actor and ask Camille to help him to be a great actor, and even go to an audition with her. He said that his face and abs deserve to be on TV or the big screen. So then Camile helps him but then he gets a part and lies to Camile that he didn't get it.
In Big Time Fans, James has a crazy fan. The fan comes up and asked him something then he says according to him in Big Time Fans, awesomeness is 15% tan, 40% good attitude, 20% bad attitude, and 50% imported hair care product. He is completely aware that this is 125%. That fan wants to be like James, think like James, and sing like James. But soon James finds himself in a dog cage then his crazy fan said "I wanna take your place in Big Time Rush, we tour the world, and I go solo. Start a movie career. Marry super hot model. Buy a yacht called S.S. Awesome." and then James replied "That's my plan!". So then Katie helps James out and James says,"Oh thank you! Thank you, thank you! He was so tiny!" and Katie says,"Can I have your autograph? I'm your biggest fan." "Sure, anything." but finds out it was a contract. "You just signed saying that I'll be your manger when you go solo, and that I have never had a crush on you. Thanks!" and walks off. "I've gotta stop giving out autographs."
Basically, James wants to become famous, but he finds himself in a bit of a hole trying to get there.
- James will meet Winnie the Pooh and his friends in Winnie the Pooh meets Big Time Rush (Full Movie).