O'Malley's campaign submitted 1,175 signatures, but only 772 of these were deemed valid, according to the Ohio Secretary of State's office. To qualify for the primary, a candidate must provide 1,000 valid signatures.
The campaign's failure to meet the Dec. 16 deadline was first reported by the Associated Press.
"Our campaign filed nearly 1,200 signatures for the Ohio ballot," said O'Malley spokeswoman Haley Morris. "While this news is disappointing, we are exploring all of our options, and Governor O'Malley will campaign vigorously in Ohio."
Morris did not elaborate on what options the campaign is exploring. She noted that O'Malley has gotten on the ballot in 18 other states to date.