The US first lady, known for her privacy and independence, had not been seen in public following a surgery last month.
In pictures posted on her official Twitter account, she was seen sitting next to President Donald Trump at a private reception for families of US soldiers killed in action.
She and Trump "were honored to pay tribute to our fallen heroes. Thank you to the Gold Star families that joined us in celebration & remembrance," the tweet said.
Melania, 48, had not been spotted since May 10, when she joined the president in greeting three American hostages released by North Korea.
Shortly afterwards, she entered Walter Reed National Military Medical Center for what the White House said was a benign kidney procedure.
Despite the operation's routine nature, Melania remained there for five days, returning to the White House on May 19.
On Sunday, her spokeswoman Stephanie Grisham confirmed that the first lady will not accompany the president to the G7 summit in Canada or the North Korea nuclear summit in Singapore.
Her recent schedule has seen a noticeable shift from the weeks prior to the surgery, when she engaged in several high-profile events.
In April, she represented the Trumps at former first lady Barbara Bush's funeral, rolled out her "Be Best" awareness campaign to help children, and orchestrated an elaborate state dinner for the Macrons of France.
Following the surgery, Melania's absence at events where the public has come to expect her alongside the president was well documented, leading her to take to Twitter to castigate reporters.
"I see the media is working overtime speculating where I am & what I'm doing," she tweeted last week, assuring she was "here at the @WhiteHouse w my family, feeling great, & working hard."
The tweet sparked a conspiracy theory that Trump himself may have written Melania's message, given that "working overtime" is a favorite phrase of the president when he tweets about the press.
Spokeswoman Grisham dismissed the media speculation as "nonsense."
Imagination 'running wild'
White House silence, including about why Melania spent five days in hospital for a routine procedure, only fueled the speculation.
Some said Melania had moved back to New York or was cooperating with special counsel Robert Mueller, head of the main investigation into alleged Russian election meddling that President Trump has branded a "witch hunt."
Others offered she may be healing after some secret plastic surgery.
Such a weeks-long disappearance by a modern-day first lady is indeed rare, said Ohio University history professor Katherine Jellison, an expert on presidents' wives.
"I'm amazed Mrs. Trump has been able to do it," she told AFP.
The first lady is not an elected position, and Melania Trump is under no obligation to keep the American people abreast of her health, activities or whereabouts.
Several 19th century first ladies spent long periods out of view. But over the past half century, it has become the expectation that people know the basic narrative of the first lady's activities.
Melania Trump, never one to obsess like her husband about media attention, has laid low before.
She went quiet in March as a media storm raged about revelations that her husband's lawyer paid porn star Stormy Daniels $130,000 before the 2016 election to keep silent over her alleged affair with Trump years earlier.