Parrott said he is considering launching a petition drive to put the death penalty ban on the ballot for voters to decide in 2014.
"We are thinking about it," Parrott said, noting that an announcement could come as soon as Friday.
State Sen. Jamie Raskin, a Democrat and constitutional law professor who opposes the death penalty, said he believes pressure is building around the country to focus law enforcement resources on things that are proven to lower the homicide rate.
"The trend lines are clear," Raskin said. "There's nobody who's adding the death penalty to their state laws. Everybody is taking it away."
Opponents of capital punishment also noted that the state won't have to worry about potentially putting an innocent person to death. Kirk Bloodsworth, a Maryland man who was the first person in the U.S. freed because of DNA evidence after a conviction in a death penalty case, attended the news conference.
The bill will not apply to the five men the state has on death row, but the governor can commute their sentences to life without parole. O'Malley has said he will consider them on a case-by-case basis.
The state's last execution was in 2005, when Republican Gov. Robert Ehrlich was in office.
Last year, the Death Penalty Information Center said in an annual report that just four states carried out more than three-fourths of the executions in the United States last year, while another 23 had not put an inmate to death in 10 years.