Final details of the contract are still being finalised, but JLP head of press and PR Helen Dickinson confirmed Tulchan had been selected after a competitive pitch.
The decision to hire external help has been prompted by the departure of corporate press and PR officer Greg Williams to become head of press at the Corporation of London.
'For many years Greg spoke to journalists on corporate matters. With his departure we realised we had a gap in this department and the majority of companies have support on this,' said Dickinson.
She added that the decision to take on financial PR help did not hint at potential changes to the Partnership's privately-owned status, but was due to the complexity of the firm's financial structure.
Tulchan founder Andrew Grant added: 'Although it is a private company, it is to all intents and purposes treated as a public company by the media.'
Tulchan's work on the account is headed by Grant and consultant Kate Inverarity, who report in to Dickinson at JLP.