Aitchison is a Singapore Permanent Resident, and the Australian has been living in Singapore since 1983. Before he became a full-time writer, Aitchison was a voice actor, and creative director of an advertising agency. He has also published books on business and advertising.

Under the pseudonym of James Lee, Aitchison's Mr. Midnight series has captivated young readers since 1998, with over 1.5 million copies of Mr. Midnight books sold. The books are horror fiction stories with different characters featured. Readers are invited to send in their stories, which Aitchison then fleshes out in his books. His publisher, Flame Of The Forest, came up with the idea of publishing an Asian series of horror and suspense stories for children, using Asian names and backdrops. It wanted to provide children in the region with reads that they could identify with, a change from books from the West that centred on white children. The Mr. Midnight series was sold to other Asian countries such as Malaysia, Hong Kong, China, Thailand, Indonesia and Vietnam

In March 2006, Aitchison launched the Mr. Mystery series, books catering to the same demographic group, with murder mystery stories solved by a group of characters.

In June 2009, Aitchison launched a new series called The Young Immortals, centering Three kids- Train Tang, Jeffry Hunter and Tamaryn.

Aitchison's other works include the Sarong Party Girl series (1994, 1995, 1996), The Seriously Funny Anti-Stress Book (1995), and Terror In Bali: An Eyewitness Account (2003). He also wrote the national songs "One People, One Nation, One Singapore" and "My Singapore Story" for the National Day Parade.