Instead, Topp says he wants to run in Quebec, the province that delivered more than half the NDP's 103 seats last May and vaulted the party into official Opposition status for the first time in its history.
Topp, the presumed front-runner in the race to succeed Layton, had flirted with the idea of running in Toronto-Danforth, but the timing was always problematic.
Prime Minister Stephen Harper must call a byelection in the riding by Feb. 22, a month before New Democrats are to choose their new leader on Mar. 24.
Topp now says he wants to focus on the leadership contest until it's over.
After that, he says his strong preference is to look for an opportunity to run for a seat in Quebec, the province where he was born and cut his political teeth, although he now lives in Toronto.
Topp says he's chosen Quebec because maintaining the NDP's breakthrough in the province "is fundamental to defeating and replacing Mr. Harper in the next election."
Should Topp win the leadership, his preference for a Quebec seat could leave the NDP leaderless in the House of Commons for as long as three years, until the next election in the fall of 2014. There are currently no vacancies in Quebec.
Topp declined to say if he'd ask one of the NDP's 59 Quebec MPs to step aside in order to pave his way into the Commons quickly.
"I'll deal with this after the leadership race, in the circumstances as they will then lie -- with an eye to getting into the House as quickly as possible," Topp said in an email.
Topp is supporting Craig Scott, a law professor and human rights activist, for the nomination in Layton's old riding.
Layton's one-time constituency assistant, Claire Prashaw, is also seeking the nomination.
Topp is the only one of the leading contenders to succeed Layton who has never sought elected office. He has said he'll run in the next election, whether or not he wins the leadership.