The talented striker, who was understood to be in talks with a number of English clubs regarding trials but has decided to move to City and is expected to sign on the dotted line after his medical on Monday.
"I'm delighted to be signing for Derry City they are a big club and I'm expecting us to be challenging for honours," said Stewart.
The 21-year-old also admitted to Sentinel Sport that he can't wait to get to play his first game for City.
"Although I'm signing on Monday, I still can't play until early July, however I haven't been playing for a few weeks now, so it might take me a while to get back to match fitness.
"Nevertheless I think with full-time training then I won't be too far behind the rest of the squad whenever I'm cleared to play."
The former Linfield man, who previously played for Wolverhampton Wanderers, also admits when the Setanta Sports Cup restarts in September he'll be disappointed that he'll have to watch the game from the stand.
"I think having signed for Derry means I'm cup-tied for the competition, so I'm disappointed I can't play against my old club.
"I enjoyed my time at Linfield, they are a big club but that's finished and although a few clubs were talking to me I have decided to sign for Derry City and I can't wait to play at the Brandywell."