Daniel Archibald Frank, 30, has been charged with one count each of assault and breach of probation after allegedly attacking his ex-girlfriend as she recuperated in the hospital's maternity ward on Saturday.
The baby was not injured during the altercation.
Police found Frank in downtown Nanaimo several hours after the assault was reported, and arrested him without incident.
Alcohol may have contributed to the incident, police said.
RCMP Const. Gary O'Brien said Frank was on probation for domestic assault and is now under strict instructions not to see his ex-girlfriend.
"It's very standard in situations where there is an assault ... to have no contact with the victim," O'Brien said.
"If any other factors — drugs and/or alcohol — came into play, they would be excluded as well. So that person, of course, could not consume alcohol."
Neither the new mother nor the baby have been identified.