He estimated that the move will bring 161,000 additional people into the low-income health insurance program, which is run jointly by states and the federal government.
Costs for the expansion will be covered entirely by the federal government through 2016.
Colorado can expect to pick up 10 percent of the tab by 2020 using the proceeds from a Medicaid provider fee that began in the state after being enacted in 2009.
The Supreme Court decision to uphold the healthcare law made its Medicaid expansion optional for states. Many Republican governors have refused to enroll more of the uninsured, citing costs.