In its latest version of Economic Outlook report, the Paris-based agency revised down world economy to 3.5 percent in 2019 from an initial forecast of 3.7 percent.
"Trade conflicts and political uncertainty are adding to the difficulties governments face in ensuring that economic growth remains strong, sustainable and inclusive," said OECD Secretary-General Angel Gurria.
"We urge policy-makers to help restore confidence in the international rules-based trading system and to implement reforms that boost growth and raise living standards - particularly for the most vulnerable," he added.
In its outlook, the think-tank found that trade tensions have shaved between 0.1 and 0.2 percentage points from the global growth this year.
Noting very low interest rates in many countries - particularly in the euro area - and the historically high debt-to-GDP levels, the OECD urged coordinated action focusing on growth-friendly measures, such as investment in physical and digital infrastructure and targeting consumption spending more towards the less well-off.
"There are few indications at present that the slowdown will be more severe than projected. But the risks are high enough to raise the alarm and prepare for any storms ahead. Cooperation on fiscal policy at the global and euro level will be needed," said Laurence Boone, OECD Chief Economist.