Late-night talk show host Jay Leno took a 50% pay cut as part of NBC's budget-chopping effort last month at "The Tonight Show," the network said, detailing the scope of the changes for the first time as well as the reasoning behind them.

The outsized pay cut, which took Mr. Leno's salary down to around $15 million, helped NBC slash the show's $100 million annual budget by about 20%, the network said. At the same time, Mr. Leno, the leading late night host, extended his contract...