Schieffer will serve "for a short transition period" until the broadcast gets a new format, CBS News President Andrew Heyward said.
CBS Chairman Leslie Moonves said last month that he was probably going to install a multi-anchor format for the "CBS Evening News," which has been a distant third in the ratings behind NBC and ABC.
CBS is part of Viacom Inc., while NBC is owned by General Electric Co. and ABC by The Walt Disney Co.
The Schieffer announcement confirms that the new format won't be ready in time for Rather's exit March 9 — the 24th anniversary of when he took over from Walter Cronkite.
A Texan like Rather, the amiable Schieffer is usually his right-hand man on Washington stories. He has led "Face the Nation" since 1991, making it competitive for second place behind NBC's dominant "Meet the Press." He anchored the Saturday edition of the "CBS Evening News" for 20 years until 1996.
He has covered every presidential campaign and been a floor reporter at all of the Democratic and Republican National Conventions since 1972. He was also the moderator last fall for one of the three presidential debates between President Bush and John Kerry.
Schieffer joined CBS News in 1969 and has been chief Washington correspondent since 1982.
There seems little chance the evening news role would turn permanent. Moonves said last month he favored revolutionary, not evolutionary change in how the evening news does things, because of the poor ratings and the news division's National Guard scandal. Rather was faulted for his role in last fall's ill-fated story about President Bush's military service, for which the network is ousting four news division staffers.