By giving additional markets to Sinclair, the deal could create another headache for conservative rival Fox at a time when Rupert Murdoch's broadcast empire is grappling with allegations of sexual harassment.
Sinclair will acquire 100 percent of Tribune shares for $43.50 each, also assuming approximately $2.7 billion in net debt, the companies said.
Shares of Tribune closed up more than 5 percent following the announcement. Sinclair's stock closed down 2 percent.
The deal, expected to close by the fourth quarter, will give Tribune stockholders $35 in cash and 0.23 shares of Sinclair Class A common stock for each share of Tribune Class A common stock and Class B common stock they own.
"This is a transformational acquisition for Sinclair that will open up a myriad of opportunities for the company," Sinclair CEO Chris Ripley said in a statement. "The Tribune stations are highly complementary to Sinclair's existing footprint and will create a leading nationwide media platform that includes our country's largest markets."
Reuters had reported on Sunday that the two companies were close to finalizing a deal. The $43.50 per share offer represents a nearly 8 percent premium to Tribune's closing price on Friday.
Tribune Media has 42 owned or operated broadcast stations, as well as cable network WGN America, Tribune Studios and WGN-Radio. Sinclair, which has a market capitalization of $3.36 billion, owns, operates or provides services to 173 television stations in 81 markets.
The announcement comes weeks after the Federal Communications Commission voted to reverse a 2016 decision that limited the number of television stations some broadcasters can buy.
To comply with FCC ownership requirements and antitrust regulations, Sinclair may still sell certain stations in markets where it currently owns stations.
The Tribune's newspapers, including the Chicago Tribune and Los Angeles Times, were spun off into a separate company, Tribune Publishing, in 2014. The company has since been renamed to tronc.
—Reuters contributed to this report.