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 was part of the 'YouTube Boyband' that raised money in 2014 for Comic Relief and was featured in The Guardian. He was named by Yahoo! News as one of "12 Web-savvy entrepreneurs to watch" in December 2013. In 2014 he starred, along with a number of other YouTubers, in the Style Haul series The Crew, described by teen website Sugarscape.com as "the male version of Loose Women, but a bit less pervy". He featured in a 2014 episode of the American television series Web Therapy.Lee has over 6.1 million followers on Twitter and over 3.6 million on Instagram, as of April 2018.Lee played a character named Garlic in the comedy movie Spud 3: Learning to Fly, alongside fellow YouTuber Troye Sivan. In the UK version of the 2015 movie The SpongeBob Movie: Sponge Out of Water, he played the voice of a seagull. Lee and Joe Sugg are featured in a 2015 travel documentary, Joe and Caspar Hit the Road, and its sequel Joe and Caspar Hit The Road: USA, produced for BBC Worldwide. Also in 2016, Lee starred in Laid in America alongside YouTube comedian KSI (Olajide Olatunji).Lee appeared in the music video for Charli XCX's 2017 single, Boys.In August 2017, it was announced that Lee would become Chief Innovation Officer of Influencer Ltd, a British influencer marketing agency.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.