Former Federal Deposit Insurance Corp. Chairman Sheila Bair plans to endorse Elizabeth Warren, a Democrat, in her race to capture a Senate seat in Massachusetts.

Ms. Bair, a Republican, said she has never campaigned for a Democrat before but felt strongly that Ms. Warren would do a good job if elected to the post. The two worked together during the financial crisis, often arguing for more government programs to help homeowners and consumers.

“I have confidence in her independence,” Ms. Bair said. “We don’t agree on everything, but I value her independence and her commitment.”