Sinclair has been in fine form for Swansea this season, scoring 12 goals and helping Brendan Rogers' side to third place in the Championship.
"Playing every week I'm getting more confident as the games go on and hopefully I can take that into the international stage," Sinclair told the club's official website.
"I'm really delighted with the call-up. It's an honour to play for your country. To get into any international age group - under-18s, 19s or 21s - is a massive honour for any player and I'm really excited about it.
"It's also an honour to play for Swansea and everyone can see the way we play football is really paying off."
Source: PA
Source: PA