Speaking at a campaign fundraiser in Memphis, Tenn., Mrs. Obama urged supporters to help boost the law's popularity ahead of the November presidential vote.
"When it comes to healthcare, please, please tell people about the historic reform this president passed," she said. "Tell them that today's Supreme Court decision was truly a victory for families all across this country.
"Because of this reform, help them understand that insurance companies will have to cover preventative care for things like contraception, cancer screening, prenatal care… Insurance companies will no longer be able to cap your coverage because you're 'too sick' … [or] deny you coverage just because you have a preexisting condition," she said.
Most Americans - 52 percent - have an unfavorable view of the law overall, according to the latest ABC News/Washington Post poll. Only 36 percent view it favorably.
Many individual aspects of the law, however, including those listed by Mrs. Obama, are broadly popular, other polling has shown.
The first lady spoke at the Cook Convention Center in Memphis, her 36th reelection campaign fundraiser of the year. Around 300 guests paid $500 or more to attend, a campaign official said.