After joining Johnny's Jr., he began performing together with J.J.Express as one of the five original members along with Kouhei Matsumoto, Takumi Yamashita, Yuta Tamamori, and current Hey!

He continued his junior work and was cast in the drama Primadam in 2006, and towards the end of the year, he was chosen to be part of Tap Kids, a Johnny's Jr. group, along with Noriyuki Kanda.

On September 24 of that same year, during a live television event from the Johnny's Jr's concert in Yokohama Arena, it was announced that the group would debut under a new name, Hey!

The debut single was released on November 14, titled Ultra Music Power, and also took first place on the Oricon charts.

Nakajima appeared as Koji Kobayashi in NTV's comedy drama Perfect Son with his groupmate Ryosuke Yamada, which started on January 14, 2012.

[7] On July 10, 2012, his appearance on the August issue of Fine Boys Magazine also marked his entrance in the professional world of modelling.

In January 2013, he co-starred in the TV drama Sharehouse no Koibito alongside Mizukawa Asami and Oizumi Yo.

He then played another supporting role in the summer TV drama Hanzawa Naoki starring Masato Sakai, which started on July 7, 2013.

In the spring of 2014, Nakajima was announced as part of the big-cast drama series Yowakutemo Katemasu starring his agency's senior and Arashi member Ninomiya Kazunari.

Nakajima started 2015 with a hit romantic comedy drama Date starring Watanabe Anne and Hasegawa Hiroki.

That same month, it was announced that he will star his very first movie, Pink to Gray, a novel adaptation written by his agency's senior and NEWS member Shigeaki Kato.

On October 1, 2015, Nakajima, along with co-star Suda Masaki and director Yukisada, flew to Korea for the world premiere of the said movie in Busan International Film Festival.

The movie and Nakajima's portrayal received generally positive reviews, with a current rating of 95% on Rotten Tomatoes.

He is also set to appear as the co-lead in the KTV/Fuji Television live-action drama adaptation of the manga of the same name The Top Secret, playing two roles: Aoki Ikko and Suzuki Katsuhiro.