MSPs have voted in favour of pushing for proportional representation (PR) instead of the "first-past-the-post" system.
Green MSP Robin Harper, who is standing as a Westminster candidate on 6 May, led calls to change the system.
Following the 54-41 vote in Holyrood, he said: "The democratic gulf between our votes and the MPs we elect cannot continue."
Labour and the Conservatives argued against ditching the system but were overruled by SNP, Liberal Democrat and Green votes.
Holyrood's two Green MSPs – both elected because of proportional representation in Scotland – favour introducing the single transferable vote system, already used in Scottish local government elections.
Mr Harper said: "So-called strong governments, elected with minimal support, may suit the old parties who can then ram through their agenda without scrutiny."