Israel's Channel 10 TV reported Netanyahu as telling the court that if Israel were to alter its deal investors could turn away and buy gas from Israel's enemies instead.
Netanyahu said he chose to speak in court because of the strategic importance of the gas deal, which he says will allow Israel to develop ties with Jordan, Egypt and Turkey and significantly boost its economy.
Sunday's decision gave parliament a year to amend the plan or the framework will be canceled.
Netanyahu has made the gas deal a centerpiece of his agenda, saying the discovery of large reserves would bring energy self-sufficiency and billions of dollars in tax revenues.
Critics have said the deal gave excessively favorable terms to the government's corporate partners.
Resource-poor Israel announced the discovery of sizeable offshore natural gas deposits about five years ago, and a partnership of Israeli and U.S. companies, including Texas-based Noble Energy and Israel's Delek Group — have already begun extracting some reserves.
Resource-poor Israel announced the discovery of sizeable offshore natural gas deposits about five years ago.
A partnership between Noble Energy and Delek Group, which is led by billionaire Yitzhak Tshuva, is the main developer at Israel's two larger gas fields, Tamar and the heftier Leviathan.
After the country's antitrust commissioner determined the gas companies' ownership constituted a monopoly, a government committee reached a deal with the firms to introduce competition.
Opponents later challenged the deal in court because they said it favored the developers over the Israeli public.
Opposition lawmaker Shelly Yachimovich, a leading opponent of the deal, tweeted that Netanyahu's speech was full of "exaggerations, clichés and general statements without one fact behind them."