Judged by the usual criteria, Greg Hall should be the obvious choice to fill the vacant seat from Prince George’s County in the Maryland House of Delegates caused by the removal of the incumbent, Tiffany Alston, for corruption. When he ran for the Maryland General Assembly in 2010, Mr. Hall was the runner-up; he finished fourth in a race for three seats representing House District 24, which includes Landover, Capitol Heights, District Heights and Seat Pleasant.

But Mr. Hall, has a checkered past. It includes, prominently, a rap sheet dating from his time as a crack dealer 20 years ago.

For a time, he faced a murder charge, and spent 40 days in jail, stemming from a 1992 gun battle in which an innocent 13-year-old boy was killed in crossfire. Although that charge was dropped, and a jury found that another gunman fired the fatal shot, Mr. Hall was convicted separately of a misdemeanor gun charge.

Those are the reasons cited by Gov. Martin O’Malley for refusing to follow the lead of Prince George’s Democratic Central Committee and appoint Mr. Hall to fill the vacant seat in District 24. Although Maryland’s Constitution gives the governor only a rubber stamp in this instance, he has balked, in defiance of the Constitution’s clear language. So Mr. Hall’s appointment is now before a state court.

Maryland politicos assume that Mr. O’Malley is worried that the appointment could cause him grief if, as expected, he runs for president in 2016. Perhaps.

But whatever the governor’s thinking, he’s wrong on the merits. Mr. Hall’s criminal past was half a lifetime ago — he is now 42 years old; his misdemeanor conviction occurred when he was 21. More to the point, he’s made something of himself, maintaining a home with his wife, an elementary school principal, and her two children; running a small business; working for local Democratic politicians; and, at the behest of prosecutors, speaking frequently to groups of wayward youths and ex- offenders about rebuilding a life after his mistakes.

None of that proves Mr. Hall would necessarily be an effective lawmaker, and none of it makes him a model citizen. He’s had financial problems and is working to pay off at least $9,000 in back taxes. He also has been charged twice with buying cars at auction with invalid temporary tags. (Both cases were dropped.)

But by every account, Mr. Hall has taken responsibility for his past. He’s gone out of his way to be engaged with his community, and he’s done a good deal more than many ex-convicts to make amends. He’s played by the rules — rules set by the state Constitution, not Mr. O’Malley — and deserves a chance to serve out the remaining two years of Ms. Alston’s term.

That’s not just a question of redemption; it’s a matter of law and fairness. And if Mr. Hall proves unworthy in office, the voters will have a chance to fire him in 2014.