The 25-year-old is Irish-qualified through his paternal grandfather who was originally from Belfast and through the Exiles, he has represented Ireland at Under-18, Under-19 and Under-21 level.
He joined the Worcester Academy straight from college and burst onto the senior scene towards the end of the 2008/09 season.
In all he has made 50 appearances in the front row for the club and has had loan spells at both Otley and Plymouth.
Commenting on his move to Ulster, Black said: "This is a new and exciting challenge for me. I'm at the stage in my career where I'm looking to really push on and I'm really looking forward to playing in the Magners League and Heineken Cup.
"I've watched Ulster this season and been very impressed with how the team is developing and I'm looking forward to being part of that.
Mike McComish will join Ulster from Connacht where he has played for the past two seasons. He is an accomplished number 8 but can play anywhere in the back row.
A former Development player within the Ulster squad, he had spells with both Rotherham and Otley in England before joining Connacht ahead of the 2009/10 season.
McComish attended Campbell College and went on to impress with Ballymena in the upper reaches of the All-Ireland League.
The 27-year-old has played for Ireland at Under-21 level and also represented the Ireland Sevens side at the Rugby World Cup Sevens in Hong Kong in 2005.
Ulster's Operations Director David Humphreys said: "We're delighted to announce that Callum and Mike will be joining us and strengthening our squad ahead of next season.
"Having spent the last few seasons with Connacht, Mike has gained a lot of Magners League experience, while Callum has experience from the Premiership, the Championship as well as the LV= and Amlin Challenge Cup competitions and so will be a very useful addition to our front row."