MEP is handed top role.
She has been elected as the leader of the UK's Liberal Democrat delegation in the Parliament.
Mrs Hall was re-elected for a second term in June as a North-east Euro MP.
She said: "I am very honoured to be elected leader of the UK Liberal Democrats in Europe and look forward to having increased influence in representing the interests of our region."
Mrs Hall will head a very strong delegation as Lib Dem MEPs have secured some key positions in the European Parliament including the chairman of the Economic and Monetary Affairs Committee and vice-president of the Parliament.
She said: "Liberal Democrats will use our strength to fight for an open and transparent Parliament that gets real results for citizens.
"I am looking forward to leading our team at the start of a challenging new mandate."
Nick Clegg MP, leader of the Lib Dems in the UK, said: "Fiona is a woman of immense integrity and deeply held convictions.
"I am very much looking forward to working with her to create a Europe that helps people through the recession, tackles international crime and is transparent and accountable in all that it does."