The Fed's Open Market Committee will issue its final post-meeting statement of the year at 2 p.m. ET. It is widely expected to announce the first interest rate hike since 2006. That expectation has been based on Fed Chair Janet Yellen's repeated statements that she'd like to see rates rise before the end of 2015, and a slew of recent data points.
Gundlach had warned in September that markets were not ready for a Fed hike at that time.
"What's fascinating about all this is one of the reasons the Fed gave for demurring about raising interest rates back in September was global financial conditions," he said. "It's fascinating how global market conditions are worse in most places than they were in the middle of September."
The market expert pointed to junk bonds, bank loans, emerging-market equities, commodity prices and emerging-market debt as areas that are all down from their September positions.
"What's the purpose of raising rates today with all of these indicators weaker than they were three months ago — and you gave the reason for not raising rates primarily that these indicators were weaker?" he asked. "So I think the Fed is raising rates because they promised they would in 2015, and they just can't do it one more time: To just fail to deliver on the type of rhetoric that they've given while maintaining credibility."
U.S. equity indexes have given the Fed "a little bit of clearance" for a hike, Gundlach said, but he emphasized his belief that the central bank was not basing its decision on market indicators.