The death penalty measure was one of more than 200 approved by the governor in his second mass bill signing since the Maryland General Assembly adjourned, The Baltimore Sun reported.
While the legislation halts all future executions, five inmates remain on Maryland's death row and their sentences have not been commuted. Maryland suspended executions in 2006 when the Court of Appeals struck down rules under which the death penalty was carried out.
With repeal of the death penalty the maximum sentence for any crime in the state is life in prison without the possibility of parole.
O'Malley also signed legislation legalizing medical marijuana for pain relief in patients with serious medical conditions. Maryland is the 19th state to legalize medical use of marijuana.
Another bill signed by O'Malley makes it easier for illegal immigrants to obtain a limited-purpose driver's license. The restricted license is not valid for air travel or entry to federal buildings.