The vote late in the day Wednesday would be procedural, paving the way for future debate if approved. Reid announced his intentions on the Senate floor.
Reid's call for a vote was considered a gamble by Democrats who have been pushing for months to overturn the 1993 law, which bans gays from revealing their sexual orientation. Republicans have blocked previous attempts to advance the bill, citing procedural grounds. It remained unclear Wednesday morning whether GOP concerns had been addressed.
If the vote fails, the bill would be considered dead for the year. The repeal effort would then face an uphill battle come January when Republicans take control of the House and increase their numbers in the Senate.
Advocates for repeal said privately they thought Wednesday's vote was doomed to fail. Publicly, gay rights groups called on President Barack Obama to use his power to ensure the vote succeeded.
"The president set a course for repeal during his State of the Union address and this Senate vote may be the steepest hurdle of this 17-year fight," said Christopher Neff, deputy executive director of the Palm Center at the University of California, Santa Barbara.
"This is the president's vote and his leadership can make the difference today," Neff said in a statement e-mailed shortly after Reid's announcement.
Reid and the White House have said repealing the military ban on gays serving openly was a priority, but have not aggressively pushed the measure in Congress' lame-duck session. Instead, they have focused most of their efforts on striking a deal with Republicans on tax cuts and ratifying a nuclear arms treaty with Russia.
There are probably more than 60 senators willing to overturn "don't ask, don't tell," giving advocates a fillibuter-proof majority.
At least three Senate Republicans - Scott Brown of Massachusetts, Susan Collins of Maine and John Ensign of Nevada - have said they would support repeal. Conservative Democrats who were initially reluctant on the matter, including Sen. Mark Pryor of Arkansas, have also said they would vote to lift the ban.
But Republicans have said the Senate should consider tax cuts and government spending before moving to other issues. Even then, Republicans say, the bill would require more debate time than Reid has allowed.