“Hannity & Colmes,” the longest-running program on the Fox News Channel, will soon be without Colmes.

Alan Colmes, 58, the liberal half of the 9 p.m. show, will leave his daily hosting duties at the end of the year, the network announced Monday.

While the network remained quiet about its plans for the political debate program, two people close to the network said that Sean Hannity, 46, Mr. Colmes’s conservative counterpart for the last 12 years, would become the sole host of the hour. The people requested anonymity while speaking about private deliberations.

Mr. Colmes will remain at the network as a commentator and will develop a potential weekend program. He will also continue to host his weekday radio show, broadcast from 10 p.m. to 1 a.m. In a statement, Mr. Colmes said that he approached Bill Shine, the network’s senior vice president of programming, months ago and told him he wanted to “develop new and challenging ways to contribute to the growth of the network.”