His role will come into effect no later than June 2020.
News of the appointment follows Landsec’s announcement that it suffered a half-year loss with plunging profits.
In its trading update published last week, the group, which is the largest commercial property development and investment company in the UK, reported a loss of £368m in the value of its properties.
The period ending September 2019 saw profits fall by £147m, which lies in stark contrast to the £42m profit generated last year.
This is largely down to an increase in high-profile retail failures and administrations, which saw the value of Landsec’s properties decrease 2.8% to £13.4bn.
Robert Noel, current CEO of the group, said that the “challenging” retail market was impacted by structural change, CVAs and administrations.
He added: “With a General Election next month and the UK’s proposed exit from the EU further delayed, there will be continued uncertainty in the near term.
“However, we go into the second half of the year with confidence.”
Allan is currently CEO of regeneration specialists, St Modwen Properties, and prior to that was CEO at The Unite Group for 10 years. He is also a qualified chartered accountant, and member of the Royal Institution of Chartered Surveyors.
Chairman of Landsec, Cressida Hogg, said: “I am delighted to announce that Mark is to join Landsec as our next CEO. Mark has been a highly successful CEO of two companies in the property sector.
“He has demonstrated strong management skills and the strategic insights that we believe will build on the strengths of our business today and be invaluable for the next phase of Landsec’s evolution.”
She added: “On behalf of the Board, and all of my colleagues in the business, I welcome Mark to Landsec and look forward to working with him when he joins next year.”
Allan said: “Landsec is an iconic property company with a fantastic heritage and I am delighted to have the opportunity to lead it.
“The world of Real Estate is undergoing significant change and I am confident, with the skills and experience already in place, that great opportunities lie ahead.”
Robert Noel will continue as CEO until Allan’s appointment. His leaving date is yet to be announced.