The designer was awarded the James Smithson Bicentennial Medal at the National Museum of American History on a day which marked the 200th anniversary of the American flag, which has been a staple of the Ralph Lauren brand's iconography for years.
Hillary said during the presentation: ''Now surely Ralph and his family ... could not have imagined, or maybe they could have when they landed in the Bronx, that their lives would be the embodiment of the American dream.
''In particular, Ralph, the youngest, would become synonymous with American aspiration and style.''
Hillary wore her first-ever Ralph Lauren custom-designed outfit for the event, which included a cobalt-blue silk jacket.
The pair first joined forces when the politician was First Lady in 1998 to raise funds for the Smithsonian in order to preserve the original 'Star-Spangled Banner' flag that inspired the national anthem, along with other historic artefacts.
The designer donated $13 million to help restore the flag and to support the programme.
Hillary added: ''Ralph responded to the call. He didn't have to. But he understood because it was deep within him that part of being an American is giving back.''
Take a look back at October's inaugural event.
The film is expected to continue without Mendes' involvement.