The Corran Ferry was set to be out of action for several weeks after a series of breakdowns with residents who rely on the service, which connects Corran to the Ardnamurchan Peninsula and opens up direct road access to Fort William, facing a 40-mile detour.
Highland Council, which runs the service, has been in talks with the Scottish Government after appealing for military assistance, with a request now made to the MoD for help.
Ian Blackford, MP for Ross, Skye and Lochaber, made direct contact with Defence Secretary Ben Wallace over the issue.
Mr Blackford said an “agreement in principle” had now been reached with the MoD with some paperwork to be completed. He hoped the service would be up and running in “coming days”.
Mr Blackford said: “We know that other people were offering help but not to the extent that we could have deliverable services.
"I'm glad over the course of the week that we've been able to make a formal request from Highland Council with the assistance of the Scottish government that are underpinning all of this to ask the Ministry of Defence to do what they can do to get a vessel up to the Corran narrows so that we can get a service going."
The Corran Ferry, which takes passengers and their cars on a six-minute journey over Loch Linnhe, is the busiest single-vessel ferry route in Scotland and carries more than 270,000 cars each year.
A reduced service has been in operation since January while repair work is carried out on the main MV Corran. However the relief vessel, the Maid of Glencoul, broke down on Easter Friday. Highland Council said there could be no service for several weeks.