Lorna Jack is to receive £6,987 a year for the position, which typically takes up two days each month. However, she has arranged for that fee to be paid to the society.
Before joining the legal- sector body in 2009 Ms Jack had public-sector roles with Scottish Enterprise and the Scottish Council for Development and Industry.
Bruce Beveridge, Law Society of Scotland president, said: "I am delighted that Lorna has been appointed to this position, which will allow her to contribute her considerable business skills and experience to supporting HIAL's work in some of the more remote parts of Scotland.
"Lorna will take up this role in addition to her responsibilities at the Society. In recognition of the support she has received from her colleagues Lorna has arranged for her remuneration to be paid to the Society."
James McLaughlin, recently human resources director for the Nuclear Decommissioning Authority and previously group head of learning at Royal Bank of Scotland, is also taking up a non-executive role on the board at HIAL.
Both appointments will run for three years.
The publicly owned HIAL operates 11 airports, including Dundee, Inverness, Barra, Stornoway and Islay.
Grenville Johnston, chairman of HIAL, said "Lorna's financial and business experience and Jim' s strong HR background will add to the existing skills of our team.
"We are looking forward to introducing them to the world of airlines."