Elon Musk will join Twitter's board of directors with a 9.2% stake in the company, according to a report filed with the US Securities and Exchange Commission, CNBC reported.

The company's stock rose more than 6 percent in premarket trading.

Musk's term expires in 2024, according to the filing. Musk cannot be the beneficial owner of more than 14.9 percent of the company's outstanding common stock during his term on the board or 90 days thereafter.

Musk's purchase came after the company was criticized on social media. Last month, the Tesla CEO quizzed people on Twitter about free speech principles. He added that he was considering a new social media platform.

After his inclusion on the board, Musk said Tuesday that he would push for changes.

Musk's stake, though the largest among outside shareholders, is considered passive, which often means that the owner does not try to control or influence the company. Nevertheless, some investors expected Musk to take an "aggressive" stance.