Entities affiliated with Slim exercised the warrants he bought in 2009 when he loaned the company $250 million during the height of the financial crisis.
New York Times, controlled by the Ochs-Sulzberger family through Class B shares, paid back the loan in 2011.
Slim’s total stake is valued at $341.4 million, based on the stock’s Wednesday closing price of $12.28.
He follows other billionaires who have put their faith in the media business. Amazon.com Inc (AMZN.O) founder Jeff Bezos bought the Washington Post in 2013 while Warren Buffett has invested in several newspapers.
Slim acquired nearly 15.9 million shares of Class A common stock at $6.36 per share. He earlier held an 8 percent stake.
New York Times intends to use cash proceeds of about $101.1 million to buy back Class A shares.
“..This one-off repurchase program should not be viewed as a change of position about our capital allocation plans,” Chief Executive Mark Thompson said.
New York Times, which has been under pressure to replace an evaporating pool of print advertising dollars with digital ads and money from subscriptions, projected in November a further decline in advertising sales for the current quarter.