E-mail messages released in congressional investigations of the government's response show Brown was within days of resigning when Katrina hit Aug. 29, The Washington Post reported.
The e-mail also show the Bush administration knew of Brown's intent when he was recalled to Washington and removed from front-line recovery efforts in New Orleans.
Sen. Susan Collins, R-Maine, chairwoman of a Senate committee investigating the events, said Brown's plans "may explain in part his curious detachment during the Katrina catastrophe."
While Brown resigned Sept. 12, the Department of Homeland Security hired him as a consultant -- at his full $148,000-a-year salary -- to review the government's Katrina response.
Collins said she was surprised to learn that the consulting job, originally set to end Oct. 10, was extended four weeks.