Dotcom launched mega.co.nz in January, a year after his wildly successful Megaupload empire was shut down as part of a US-led investigation into online piracy.
The 39-year-old, who was arrested when armed New Zealand police involved in the US probe raided his Auckland mansion, confirmed that he had resigned as a director of Mega at an August 29 board meeting.
"Mega is in excellent hands," he tweeted. "I resigned as managing director to focus on my copyright case and a new political party."
Dotcom, who is free on bail in New Zealand pending an extradition hearing expected to take place in April next year, said he was still working on development of a web-based music service called Megabox.
The extradition case has dragged on in the courts and is subject to numerous appeals, with Dotcom estimating earlier this year that his legal bills could exceed US$50 million.
He announced plans this week to launch a political party to contest next year's New Zealand election, which will attempt to prevent conservative Prime Minister John Key winning a third term.
Dotcom has been a fierce critic of Key, whom he accuses of bowing to Hollywood pressure by pursuing the piracy case against him.
The party is set to be launched on January 20 next year, the second anniversary of the raid on Dotcom's home. He cannot stand for parliament directly because he remains a German national, but intends to serve as the party's president.