Commentators noticed similarities with Mrs Obama's 2008 convention speech.
Mrs Trump's speech also praised her husband as a "compassionate" man who would "fight for the country".
It was her first speech of the campaign and she had the help of a speechwriting team.
Mr Trump's communications adviser Jason Miller issued a statement saying: "In writing her beautiful speech, Melania's team of writers took notes on her life's inspirations, and in some instances included fragments that reflected her own thinking.
"Melania's immigrant experience and love for America shone through in her speech, which made it such a success."
Meanwhile Mr Trump himself described her speech as "absolutely incredible".