The UK's second busiest airport announced it will prepare a planning application seeking permission to bring the airstrip into full passenger use. It insisted the measure aligns with the Government's policy of "making best use of existing runways".
The West Sussex airport first suggested it could use the emergency runway to increase its capacity in October last year.
A final version of its "master plan" published on Thursday provided more details of the proposal.
The emergency runway could be operational by the mid-2020s and would be used for departures only.
Operating as a two-runway airport would enable Gatwick to accommodate up to 109,000 extra flights a year.
Gatwick lost out to Heathrow in a bid to obtain Government approval to build an additional runway, amid a need for more airport capacity in the South East.
The centre lines of Gatwick's main and emergency runways are separated by 198 metres.
The plan involves increasing the gap by widening the emergency runway by 12 metres to comply with safety regulations.
Gatwick chief executive Stewart Wingate said a 12-week public consultation shows there is "strong support for Gatwick and the local area's ambitions".
He went on: "The plans would deliver additional capacity for Gatwick, which will provide choices for the future - including incrementally growing our airport to meet demand and continuing to provide solid operational performance for passengers and airlines.
"Gatwick's global connections are needed more than ever but as we take our plans forward, we must do so in the most sustainable and responsible way, and in full partnership with our local councils, communities, passengers and partners."
Local campaign group Communities Against Gatwick Noise Emissions claimed the plan would lead to "a second runway by stealth" and accused the airport of being "the neighbour from hell".
In order to gain planning permission to routinely use the stand-by runway, Gatwick must follow the Development Consent Order process that culminates in a final decision by the Transport Secretary