Drogheda based Mr Carroll is likely to contest the next General Election for the party in Louth where his colleague Ceann Comhairle Seamus Kirk will now be automatically returned.
Two other vacancies remain in the Seanad following the election of Labour's Alan Kelly and the recent death of Fianna Fail's Peter Callanan.
The electorate in bye-elections in the upper house is confined to members of the Oireachtas so Government candidates are virtually sure to be returned.
