The former Maryland governor's criticism of the Democratic presidential front-runner came hours after Clinton told a crowd in New Hampshire that the death penalty has been applied "in a discriminatory way"
-- but said she doesn't support abolishing it.
In an interview with CNN's Dana Bash, O'Malley touted Maryland's move to repeal the death penalty -- saying it is "not a deterrent to violent crime" and "can't be administered fairly."
"Secretary Clinton is often a bit behind the times in terms of actually what works when it comes to policy," O'Malley said. "I respect her. I have a great deal of respect for her, but she's often late to many of these issues because she's of a different generation than I am."
Clinton has long backed the death penalty -- saying in her 2000 run for Senate that it had her "unenthusiastic support" and maintaining that position in her 2008 run for president.
But she waded extensively into the issue Wednesday in New Hampshire, addressing a topic that she hadn't yet been asked about during the 2016 campaign.
"I think that we have a lot of evidence now that the death penalty has been too frequently applied and very unfortunately in a discriminatory way," Clinton said at Saint Anselm's College. "So I think we have to take a hard look at it and a lot of states are doing that."
Clinton said that the United State needs to be "smarter and more careful" about how the death penalty is applied, but that in some "egregious" cases, capital punishment is still needed in "very limited and rare" instances.
In the interview, O'Malley also criticized Clinton for her Wall Street reform proposals, which he called "little more than a smokescreen."
"When Lloyd Blankfein, the head of Goldman Sachs, tells you he'd be fine with either (Jeb) Bush or Clinton in the White House, that should tell all of us that she does not have the independence that people are looking for in their next president to protect Main Street's economy from Wall Street's excesses," he said.
Clinton said Tuesday night on Stephen Colbert's "Late Show" that she would allow banks to fail
rather than bail them out as the U.S. government did in 2008.
But O'Malley said Clinton's policy proposals are not "really a serious effort to do anything about it."
"One can understand why she's traditionally just always been very close to Wall Street and what people want in the White House is someone with the independence to stand up for our country's interests, not for the best interests of Goldman Sachs or JP Morgan," O'Malley said.