The body, which for the 18 years of its existence has only allowed public affairs consultancies and staff, will introduce the changes in January.
Changes at the APPC come following efforts to work with others in the industry informing plans for a statutory register of lobbyists.
The chairman of the APPC, Michael Burrell, said the changes had followed ‘expressions of interest’ from in-house practitioners.
He revealed the move would mean minor tweaks to the code of conduct, but stressed that ‘the substance' would remain the same.
He added: ‘The statutory register will increase transparency but government proposals do not include regulation, so that’s where we have a role to play.
'We have also been arguing that the statutory register should be as broad as possible and include in-house people, so it would be odd for us to not include them ourselves.'
Work around a statutory register was taken over from Mark Harper by Chloe Smith earlier this year as part of a Cabinet reshuffle.