Just in time for the closing rush of the presidential election, MSNBC is shaking up its prime-time programming lineup, removing the long-time host –- and one-time general manager of the network — Dan Abrams from his 9 p.m. program and replacing him with Rachel Maddow, who has emerged as a favored political commentator for the all-news cable channel.

The moves, which were confirmed by MSNBC executives Tuesday, are expected to be finalized by Wednesday, with Mr. Abrams’s last program on Thursday. After MSNBC’s extensive coverage of the two political conventions during the next two weeks, Ms. Maddow will begin her program on Sept. 8.

MSNBC is highlighting the date, 9/8/08, connecting it to the start of the Olympics on 8/8/08, as a way to signal what the network’s president, Phil Griffin, said “will be the final leg of the political race this year.” He added, “We making that Rachel’s debut.”

Mr. Abrams, who is well liked at MSNBC, is expected to remain at both that network and at NBC News, where he is the chief legal correspondent. He will also serve as an anchor during some of MSNBC’s daytime coverage, as well as a substitute host on NBC’s “Today” show, Mr. Griffin said.

The addition of Ms. Maddow as prime-time host had been expected for some time. Only a month ago, Mr. Griffin said she was at the top of the list to get a show at the network, and would likely get one soon.

MSNBC has put heavy emphasis this year on presidential election coverage (it has given itself the tag line, “The Place for Politics”) and has turned to Ms. Maddow frequently both as a guest and as a substitute for the network’s most popular host, Keith Olbermann. Mr. Olbermann’s emergence as the signature personality on the network has led to an unofficial rebranding of MSNBC as the liberal alternative to Fox News, which is dominated by conservative hosts like Bill O’Reilly and Sean Hannity.

MSNBC has been known to be seeking a way to capitalize to a greater degree on Mr. Olbermann’s popularity. A program hosted by Ms. Maddow will almost certainly be a closer ideological fit with Mr. Olbermann’s.

Mr. Abrams was not as overt a partisan. His program, “Verdict,” was based more in legal than political issues. He enjoyed some success, especially of late. With NBC’s Olympic coverage helping, Mr. Abrams beat Larry King’s show on CNN twice last week among the viewers preferred by news advertisers, people between the ages of 25 and 54.

Contacted by phone Tuesday, Mr. Abrams said “Putting my general manager’s hat back on, considering where the network is right now, it is actually the right call.”

Mr. Griffin said of the selection of Ms. Maddow, “This just completes our prime-time lineup. Our lineup makes sense now.”