Longmire had appeared among the top candidates to replace 2021 premiership coach Simon Goodwin, who was sacked this week.
But the Swans confirmed to AAP on Saturday Longmire would not be pursuing the role at Melbourne.
Longmire stepped down last November following last year's thumping grand-final loss to Brisbane, his fifth decider in 14 years at the helm, with Dean Cox replacing him.
He remained at the Swans, taking up the role of executive director of club performance.
It is understood Longmire is not yet ready to return to the coaching fray.
The Melbourne job is the only vacancy currently up for grabs after Carlton committed to coach Michael Voss for next season.
Buckley and Simpson now appear the clear frontrunners to replace Goodwin with Port Adelaide coach Ken Hinkley, who finishes up at season's end, indicating he won't coach next year.
Buckley spent almost a decade in charge at Collingwood, leading the club to the 2018 grand final, before departing midway through the 2021 season.
He has since taken up football commentary roles on television and radio, but has also made it clear he still has the desire to coach at the top level.
Buckley told SEN radio this week he would take the Demons' call and labelled the job "compelling", but indicated he would need to be convinced to jump back into an AFL hot seat.
Simpson, the Eagles' 2018 premiership coach, insisted to Fox Footy this week he had "refused" to entertain thinking about coaching again.
Former Essendon coach James Hird is also understood to have ruled himself out of contention.
Collingwood assistant Hayden Skipworth appears the best of the untested options, while interim Melbourne coach Troy Chaplin has confirmed he won't pursue the full-time role.
Chaplin will lead the Demons for their final three games of 2025 against the Western Bulldogs, Hawthorn and Collingwood.
While the Demons are out of the finals hunt, they can strike a savage blow to the Bulldogs' September chances if they win Sunday's game at the MCG.Â
The ninth-placed Bulldogs currently sit four points outside the top eight and realistically need to keep winning to play finals.
Melbourne have named Jed Adams to make his AFL debut, replacing Harry Sharp (omitted), while the Bulldogs go in unchanged.
