The changes will take effect on June 20, London Stock Exchange said today.
Hikma Pharmaceuticals's promotion to Britain's blue chip index comes after its shares surged 45 per cent since mid-March. The company expects its full year group revenue to be between $2bn (£1.3bn) and $2.1bn (£1.4bn).
Read more: The anatomy of a FTSE 100 chief executive
Inmarsat, on the other hand, has seen its shares fall 37 per cent since early February amid tough trading conditions in its maritime and government markets businesses.
Other companies entering FTSE 250 index include Metro Bank, Countryside Properties, Hill & Smith Holdings, Smurfit Kappa Group and Ascential among others.