Lagarde said she expects "only a modest acceleration" next year.
"The prospect of rising interest rates in the United States and China's slowdown are contributing to uncertainty and higher market volatility," she said in a speech at the Council of the Americas.
"There has been a sharp deceleration in the growth of global trade. And the rapid drop in commodity prices is posing problems for resource-based economies."
In July, the IMF pared back its 2015 forecast for global economic growth from 3.5 per cent to 3.3 per cent, citing the US economy's first-quarter stumble. The IMF's forecast for 2016 is at 3.8 per cent.
The Washington-based crisis lender is due to issue an updated forecast Tuesday to its World Economic Outlook.
"The good news is that we are seeing a modest pickup in advanced economies," Lagarde said. "The moderate recovery is strengthening in the euro area; Japan is returning to positive growth; and activity remains robust in the US and the UK as well."
She called it "not-so-good news" that growth in emerging economies is likely to slow for a fifth consecutive year, as the Chinese economy continues to slow from its once-galloping pace.
"India remains a bright spot. China is slowing down as it rebalances away from export-led growth," Lagarde said.
"Countries such as Russia and Brazil are facing serious economic difficulties."