Council President Darrell L. Clarke said Tuesday that with nearly two years left on Green's term, he would call for a special election during the May 20 primary to fill the vacancy.
The parties get to nominate their candidates - they have until April 8 - while independents must gather at least 1,785 signatures by then to appear on the ballot.
So what are the Democratic ward leaders looking for in making their pick?
For one thing, avoiding a messy fight in the Northeast, where State Rep. Ed Neilson was forced through redistricting to run against State Rep. John Sabatina Jr., a fellow Democrat and son of a powerful ward leader.
"The pulse of the ward leaders is, they don't want to see the infighting," said U.S. Rep. Robert Brady, the party chairman. "There are [other] candidates, but these guys are officeholders. One of them is going to lose his seat."
Neilson, a former political director for Local 98 of the electricians' union, was labor secretary under Gov. Ed Rendell. He could have powerful backers in his old bosses.
"I think at this time, Eddie Neilson's expertise would make him a wise choice for City Council," said John J. "Johnny Doc" Dougherty, Local 98's leader.
Neilson did not return a message left Tuesday at his district office.
Republicans, who will face a Democratic party that holds a 61/2-1 edge in registered voters, are not conceding the race, though. In fact, they have already zeroed in on a candidate.
State Rep. John Taylor, the GOP chairman, said ward leader Matt Wolfe, a lawyer from University City, was "a prominent guy" who "would be a good candidate for us."
"We'll compete," Taylor said. "Because of the offbeat nature of [a special election], you never know."
As Clarke said, May 20 is a "one-step election . . . whoever wins on that particular day will be the Council person."
The election also opens up the possibility of a prominent independent candidate taking a run at upsetting the establishment.
There has been much political chatter about finally seating a Council member from the LGBT community, or possibly adding more Latino representation. Candidates from those communities, though, may have to wait unless they are willing to launch outsider campaigns.
"I think the LGBT community has every right to have interest," Dougherty said. "I've had some conversations. . . . We'll be supporting an openly gay candidate in '15."
That's when all the Council seats are up for reelection, including the winner of the May 20 special election.
Despite the near iron grip incumbents have enjoyed on their seats, party-picked candidates didn't fare well after the last special election, in 2006.
Two of the three members elected in the special election - Carol Ann Campbell and Daniel Savage - were expelled by voters in 2007.
But that's unlikely to discourage potential candidates from lobbying for the nomination.
"Whatever's best for the party," Brady said. "No matter who we pick, somebody won't be happy."