He revealed that Leverkusen's keen interest in him made the decision easy and the club's current league position of second in the Bundesliga has justified it.
"Leverkusen showed a lot of interest in me," Carvajal told Bundesliga.com. "They told me I'd play in the first team and that I was their first choice.
"I think I made the right decision. We're second in the table, we're doing well in the Europa League and I'm playing a lot, which is what I need to keep developing as a player."
Carvajal has provided four assists and a goal so far this season for Leverkusen.