Helen Mitchell’s side have been in scintillating form throughout the campaign.
They have won 18 of their 21 league games, and have a 100 per cent win ratio from their home fixtures.
Coventry were the only team that could catch them, but were handed the penalty after fielding ineligible players.
And a statement on their website confirmed they would not be contesting the decision.
It read: "The board would like to thank all those that so generously offered legal support and expertise in defending our case; regrettably we have simply run out of time.
"We would also like to take this opportunity to congratulate all at Sheffield FC on retaining the Northern Division title."
Only one third-tier team can go up to the WSL, provided they meet FA criteria.
So although now confirmed as regional winners, Sheffield must still win one more contest – against Southern Division counterparts Portsmouth – if they are to secure promotion to the Women’s Super League Two.
The promotion play-off will take place on Sunday 24 May.