During this time, Stewart developed a passion for opera, languages, art song, oratorio, musical theater and concert repertoire, and committed himself to pursuing an operatic career.
By the end of his senior year at Juilliard, Stewart was already receiving attention from the professional classical community, was featured in the book Spirit of Harlem by Craig Marberry and Michael Cunningham, and was invited to perform one of the title roles in Acis and Galatea on tour with The Bach Society of Columbia in Germany.
He was subsequently invited to become a San Francisco Opera Adler Fellow, and numerous important debuts soon followed including: T. Morris Chester in the world premiere of Philip Glass's Appomattox; and Malcolm and Macduff in Macbeth, stepping into the latter role with only 15 minutes notice.
Stewart has been noted for the uniquely baritonal timbre of his ringing and sweet tenor instrument, as well as his innate musicality and commanding acting ability.
In Spring 2012, he made his Covent Garden debut as Hassan in Judith Weir's Miss Fortune, a role he premiered at the Bregenzer Festspiele in the summer of 2011.
He appeared in BBC Music Ambassador's concert with the Scottish Symphony, and reprised his role as Don Pedro Alvarado in Purcell's Indian Queen at English National Opera (debut), returning to Covent Garden as Pinkerton in Puccini's Madama Butterfly and making his third tour of the United Kingdom, this time in his new show "In Love Again".
In October 2016, he performed the US National Anthem at the NFL International Series' matchup between the Indianapolis Colts and the Jacksonville Jaguars at Wembley Stadium in London, UK.