Also Monday, President Obama said he "absolutely" stands by his nomination of Daschle, a former Senate majority leader who represented South Dakota in the U.S. Senate.
In the letter released Monday, Daschle offered a seven-month time line account of the particulars, saying he discovered a series of errors resulting in $146,000 in back taxes for the previous three years' returns, The Washington Post reported.
"I am deeply embarrassed and disappointed by the errors that required me to amend my tax returns," he wrote to Sen. Max Baucus, D-Mont., and Sen. Charles Grassley, R-Iowa, chairman and ranking minority member, respectively, of the Senate Finance Committee. "I apologize for the errors and profoundly regret that you have had to devote time to them."
The committee, which must vote on the nomination before it can move to the full Senate, was scheduled to meet Monday and Daschle was to be available to answer questions. The letter was released to reporters overnight, the Post said.
During an appearance before reporters Monday, Obama said he "absolutely" stands behind Daschle, the Post said.
In his two-page letter, Daschle said issues around his tax filings arose during the Obama transition team's vetting process.
"During the course of those reviews, the vetting team flagged charitable contributions they felt were deducted in error," he said, referring to $15,000 worth of donations that lacked proper receipts. Questions about other items were raised as well.
Daschle said that he "remedied these issues by filing amended tax returns with full payments, including interest."
Baucus has said Daschle paid the back taxes Jan. 2, informing the committee and White House about two days later.