The company said the larger contract relates to the maintenance of 12,000 properties in the Belfast and County Down areas. It is worth up to £366m over 10 years and will contract will commence in September this year.
The second contract is a four and a half year extension of an agreement Carillion already has with Petroleum Development Oman. It is to deliver facilities management across 12 locations that span an area of 100,000 square kilometres across Oman.
"These latest wins take the total value of new orders and probable orders for Carillion in the first six months of 2016 to around £2.5 billion, which continues to reflect the strength of our strategy and business model," said chief executive Richard Howson.
In a separate trading update, Carillion announced that the group was on track to meet expectations at the half year.
The Wolverhampton-based firm also commented that while the Brexit vote has “created uncertainty for the UK economy as a whole”, it was well-placed to deal with the fall-out of the EU referendum.
“Carillion has no significant operations in mainland Europe and prior to the referendum we undertook extensive work to assess the possible impact on our business of a vote to leave and we have put in place robust plans to manage this outcome,” Carillion said in a statement.