The fabric was developed based on the style of a men's silk tie, the White House said.
A jeweled belt that cinched the coat and her gloves were from J. Crew and her earrings were designed by Cathy Waterman. She wore Reed Krakoff boots.
The White House said her outfit and accessories will go to the National Archives at the end of the inaugural festivities.
Fashion consultant Tim Gunn told ABC News he like Michelle Obama's sense of style because she is "not a dress-up doll."
"She is of her own mind, and she knows what she looks good in," said Gunn, a longtime mentor on the popular "Project Runway" reality series.
"Thom Browne is known for avant garde menswear," Gunn said. "I thought, Mrs. Obama is wearing Thom Browne to the inaugural swearing-in ceremony, but in fact it is magnificent."