Former Labour Party rebuttal chief and ex-special adviser Adrian McMenamin has been hired as BiE head of media and research.
Nick Kent, who ran Kenneth Clarke's leadership campaign last year, has been named as head of the Tory Europe Network, a part of BiE.
And former Scotland Office minister George Foulkes has joined BiE's board.
It is understood Foulkes is tasked with combating comments made by Labour euro-sceptics and liaising closely with the Labour Movement for Europe.
BiE campaign director Simon Buckby said the appointments of experienced election and campaign professionals were vital as the group prepares for a likely referendum on the issue.
The hires come as it was announced that six cabinet members are to show support for the Europe at a BiE event at the Labour Party Conference.
McMenamin has been taken on in a temporary role covering for Jessica Bawden, who is on maternity leave.
It is understood that when Bawden returns McMenamin will carry on in an as yet unspecified campaigning role.
He headed Labour's attack and rebuttal unit in 1997 and joins BiE after resigning as special adviser to Welsh secretary Paul Murphy in July.
His resignation from the role he had held for around two years, came weeks after an early day motion tabled by Plaid Cymru and Scottish Nationalist MPs in Westminster calling for his sacking.
The motion on 21 May condemned McMenamin for allegedly making, 'irresponsible and unprofessional remarks' about the Welsh Assembly and using a computer in the Welsh Office to put out, 'party political propaganda over the internet'.
McMenamin said: 'I'm not interested in going over the past.' Although he did add that as a political appointee 'of course I was using my computer for political purposes.'