Lee started his YouTube channel 'dicasp' in 2011, and later renamed it to simply 'Caspar'. As of November 2017, Lee's main YouTube channel has over 7.5 million subscribers and over 850 million video views, and is the 243rd most subscribed channel on the website; his second channel "morecaspar" has nearly 2 million subscribers and over 116 million video views
Lee appeared in the music video for Charli XCX's 2017 single, Boys.
He has a series of videos where he comically interviews celebrities such as One Direction's Liam Payne, actor Zac Efron, Channing Tatum, and a few others.