A key adviser to Prime Minister Malcolm Turnbull helped to formalise a job transfer for the partner of Barnaby Joyce, according to new details about the controversial decision to secure the new position in a ministerial office.

The letter from Mr Turnbull’s senior governance adviser was signed on May 9 last year and gave official clearance to the new role for Vikki Campion, who was in a relationship with Mr Joyce at the time and is due to give birth to their baby next month.

The role played by the Prime Minister’s office triggered detailed questioning in Parliament last month amid an uproar over the relationship and the way the government moved Ms Campion from one office to another to manage the matter.

Barnaby Joyce and Malcolm Turnbull in Parliament during the height of the crisis over the former deputy prime minister's affair. Credit:Alex Ellinghausen

Mr Turnbull fended off questions about the transfer in Question Time on February 12 by insisting his office only had an “administrative” role in the staff changes because the Nationals made the decisions about where to appoint their advisers.