NGS Global managing partner Marianne Broadbent will appear when the inquiry resumes on Thursday afternoon.
The recruitment firm conducted a highly competitive and rigorous global talent search, said a media release in June from then trade minister Stuart Ayres announcing Mr Barilaro's appointment.
Mr Ayres resigned from cabinet and as deputy Liberal leader following a draft report by former Public Service commissioner Graeme Head, which found he was not at arm's length from the appointment.
The full report, released on Tuesday, prompted Premier Dominic Perrottet to announce bans on ministers taking up public sector jobs related to their portfolios for 18 months after they depart office.
The NSW government also amended the code of conduct to prevent ministers seeking to influence department secretaries.
NGS Global ranked Mr Barilaro below a Hong Kong-based executive but the report was revised, ranking the former Nationals leader higher.
Investment NSW chief executive Amy Brown told the inquiry the firm was asked to redo it because it did not reflect the opinion of the hiring panel.
The panel decided the Hong Kong-based woman would not be suitable because she had not lived in NSW for more than a decade.
Investment NSW managing director Kylie Bell, also on the selection panel, told the inquiry she felt there was unconscious bias against Mr Barilaro.
Ms Bell said this was potentially because NGS Global knew Investment NSW did not have any women investment commissioners, and "tried to help us along that route".
Warwick Smith, a member of the selection panel for the Americas trade role and the London agent-general, will also appear.
The inquiry has expanded its scope beyond Mr Barilaro's appointment to include all overseas trade roles.
London agent-general Stephen Cartwright's appointment, which predates Mr Barilaro's, has faced particular scrutiny.
Mr Cartwright was late to the recruitment process and was appointed after another candidate had all but secured the position.
Ms Brown described Mr Cartwright threatening to go over her head to the minister or premier as he sought a salary package close to $800,000, which she could not legally give him anyway.
Dr Broadbent will face questions about what she meant when she emailed a NSW Treasury human resources employee to inform them "we would need to massage the candidate brief for Stephen" in April last year.