Germany, Greece, Italy and Slovenia have added their names to the list of member states, according to internal EU documents – paving the way for an EU-wide policy to be adopted at a summit next week.
Momentum has built for the plan since the last European Council summit in March when just eight countries supported the move.
The commitment by Germany, Europe's biggest economy and a major polluter, is significant – given Angela Merkel's government's previous reticence.
Opinion polls suggest Ms Merkel's party faces being eclipsed by the German Green party, with environment up the agenda. Greens also did well across the continent in European elections.
Surveys across the continent, including in the UK, also suggest climate change is rocketing up the political agenda – notably in the wake of school strikes and protests by Extinction Rebellion.
Theresa May committed the UK to the 2050 target last week, claiming Britain would become the first G7 country to legislate for the target. Labour has said it would bring the target forward to 2030 and achieve it with a Green New Deal by investing in new technology.
The support for the move might bring forward action on climate: as recently as last week, the policy was expected to be kicked into the long grass at June's meeting and further discussion was pencilled in for 2020.
The rotating EU presidency – which controls the agenda at summits - is currently held by Finland, which is taking an even more ambitious approach of going carbon-neutral by 2035. Finland's new governing coalition includes the country's Green party, which notably controls its foreign ministry.
Countries in central and eastern Europe are most opposed to the plan, with Poland's hard-right government the largest opposed. The European Parliament has proposed a 25 billion euro "Just Transition Fund" to help member states with less developed economies keep up. The details of any EU-wide policy would have to be hashed out at the summit.