White House spokesman Jay Carney said Tuesday that the figure was reached by Monday's midnight deadline for sign-ups.
"The fact that the 7 million number has been reached allows us to step back and look at the sweeping, positive change that the law has ushered in to strengthen health security for every American as they go through life," Carney said.
The number could climb. People who started applying but couldn't finish before the deadline can have extra time, as do potential enrollees whose special circumstances kept them from meeting the deadline.
Obama plans to present updated numbers during a Rose Garden appearance later Tuesday.
Surpassing 7 million enrollees is a major victory for Obama's health care law. Computer glitches at the start and end of the six-month open-enrollment period had put that achievement in doubt.
The administration has not provided a demographic breakdown of the enrollment numbers and does not identify which enrollees already had insurance.
Carney argued that Republicans had run ads against the law, tried to repeal it repeatedly and their determination to do so precipitated a government shutdown last year.
"That effort could not stop this law from working," he said.
House Minority Leader Nancy Pelosi, D-Calif., said the law's major benefits are the level of benefits it requires insurance companies to provide and the affordability of coverage.
She said the law could still be adjusted to address shortcomings.
"As implementation takes place then you see where there could be correctives or improvements or refinements," she said.