The couple, who had been living in the USA on green cards sponsored by Mrs Trump, took the citizenship oath in NY.
Melania Trump - who has been vacationing with her husband U.S. President Donald Trump in Bedminster, N.J. - did not accompany her parents. "I've been a very staunch advocate against the president's policies myself as an immigration lawyer", Wildes said.
Mr Wildes defended the process by which the Knavs attained citizenship, despite the Trump administration's efforts to end "chain" or family-based immigration.
The idea that family-based immigration could be labeled as "dirty" might have a lot to do with the Knavs' son-in-law. "This is a very important example of it going right".
The couple's lawyer said they had "travailed a wonderful journey".
"They had gotten sponsored by their daughter and then once they had the green card, they then applied for citizenship when they were eligible", he said.
There are only a handful of ways that immigrants to the U.S. can obtain green cards, and the largest share of them each year are given out based on familial connections.
The Republican president argues that the system steals jobs from Americans and threatens national security, calling for a merit-based system that preferences more educated, English-speaking professionals.
They arrived and departed from a Manhattan federal building escorted by Homeland Security police.
Since initial reports emerged in February that the Knavses had obtained permanent residency in the United States, there has been a lack of clarity about when or how the couple received green cards.
The 48-year-old first lady, born Melanija, changed her name to Melania Knauss when she started modeling. She was in Bedminster, New Jersey, at the Trump National Golf Club, where Trump is now staying. Viktor was a vehicle dealer.
Melania grew up in a two bedroom apartment in Sevnica, a small city formerly under communist control. That preferential program, popularly known as the "Einstein visa", is intended for immigrants with "extraordinary ability, [who] are an outstanding professor or researcher, or are a multinational executive or manager", according to the U.S. Customs and Immigration Services.