Reports of the investment had send shares up 22 percent on Tuesday.
The U.K. investment management firm owns 85.3 million Nio shares, the company said Tuesday in a filing with the Securities and Exchange Commission.
The Baillie Gifford management firm is Tesla's largest outside shareholder, with a 9 percent stake. Tesla's largest investor is CEO Elon Musk, who owns about 20 percent of shares.
Nio's stock closed up 22 percent Tuesday at $7.39. Since Nio shares began trading on Sept. 12, the stock has traded as high as $13.80 and as low as $5.35. When it listed its shares on the New York Stock Exchange last month, the company said it plans to make cars for the Chinese market initially, but it also has ambitions to expand into Europe and the U.S.