The former Blue singer stars as Warner Huntington III opposite Sheridan Smith's Elle Woods in the critically-acclaimed production at the Savoy Theatre.
Speaking at the Thorpe Park launch of his upcoming gameshow Scream If You Know The Answer, James said of the play: "I was contracted for six months, so I end in June.
"I've been asked to extend until October but I declined it because I want to do other things. It takes up so much time. You have eight shows a week and you have no time for anything.
"It's so hard to see my daughter and have a normal life. It's not like I can just get weekends off and pop and see her, or she can come down for me. It makes everything quite hard, so no, I want some life back."
Talking about the success of the musical, he added: "We knew that it was a good show, we loved the script and we loved the idea of how it could work in a theatre, but we never knew that it would just connect.
"The irony is that it didn't work that great on Broadway, because you're taking the mickey out of American culture and Americans don't really get it. We find it funny.
"It didn't necessarily work over there, so we were a little bit... 'Will it work here?', 'Will it transpose?', and it did. It worked really well and the English audiences, they just love it."
Scream If You Know The Answer premieres on Sunday May 2 at 7pm on Watch.