As reported earlier this month, an appeal on this permit was dismissed.
That permit means the project is now good for production of up to 125 million pounds of pure copper cathode a year.
"All required state and federal operating permits have now been successfully obtained," Excelsior said today.
It added that it was now "ready to commence construction" upon the completion of its project financing plan.
"With the appeal process officially exhausted, we now have a fully permitted project that is genuinely on the cusp of achieving low cost copper production through the most environmentally friendly process available within the industry today," said the chairman of Excelsior Mark Morabito.
"I congratulate the entire Excelsior team on achieving this positive outcome, and I look forward to seeing Excelsior unlock the true value of this tremendous asset."
Gunnison is an advanced, low cost, environmentally friendly in-situ recovery copper project and remains on-track to be the next new copper producer in the United States, with initial production scheduled for 2019.
A feasibility study projected an after-tax NPV (net present value) of US$807 million and an IRR (internal rate of return) of 40% using a US$2.75 per pound copper price and a 7.5% discount rate.
Shares added just over 2% to $1 in Toronto.
Reporting by Giles Gwinnett