PARIS— Alexandre de Juniac, the chief executive of Air France-KLM, is leaving his post after struggling to push through restructuring measures aimed at boosting the competitiveness of the ailing airline group.

Mr. de Juniac will step down in July to take over as chief executive of the International Air Transport Association, or IATA, both the carrier and the world’s largest airline lobby group said on Tuesday.

Air France shares dropped more than 6% in early trading Wednesday in response to the news.

Pending approval of IATA members at their annual meeting in June in Dublin, Mr. de Juniac would take over from former Cathay Pacific Airways Ltd. ’s CEO Tony Tyler, who announced plans to retire at the end of his five-year mandate.

Mr. de Juniac departs Air France-KLM, Europe’s largest airline by traffic, amid continued uncertainty about a restructuring plan he launched in September 2014. The proposal is intended to make the airline group more competitive against budget airlines such as Ryanair Holdings PLC and easyJet PLC in Europe, and long-haul competition from rapidly expanding Middle East carriers.

Under the plan, Air France proposed to slash 2,900 jobs and close long-haul routes unless it could gain concessions from employees. Opposition to the plan boiled over last October when workers besieged senior management, even tearing the clothes off some senior executives.

Talks between the airline and union about job cuts are continuing.

Air France-KLM in 2015 delivered its first net profit in eight years, though largely as a result of a sharp drop in fuel costs. The airline’s annual fuel bill fell €446 million ($508 million) last year, helping it deliver a €118 million net profit.

Since taking the top post at the French arm of Air France-KLM in 2011, Mr. de Juniac carried out cost-cutting plans to refocus on its low-cost unit, Transavia. He took over as CEO of the entire group in 2013.

The Franco-Dutch airline group has been losing ground to rivals, though. British Airways parent International Consolidated Airlines Group SA last year reported a €1.5 billion net profit. IAG delivered an adjusted operating margin of 11.2%. Air France-KLM’s comparable figure was 3.1%.

Air France-KLM also remains hobbled by debt, which still stood at €4.3 billion at the end of last year even after it pared the total by €1.1 billion in 2015.

The airline also has cut some of its plan to purchase planes due partly to uncertainty over its growth prospects.

Despite his struggles in turning around Air France-KLM, Nomura analyst James Hollins said Mr. de Juniac’s departure likely would be viewed negatively by investors, by whom he is well regarded. Air France-KLM’s board has hired a recruitment consultancy to help with the search.

A new chief executive could provide new momentum to the reform drive, though, Mr. Hollins said and “inject a deeper sense of urgency across the group for the need to deliver meaningful cost cuts and strategic progress with Transavia.”

Mr. de Juniac, who will be the first leader of a French airline to take the top job at IATA, becomes head of the trade body at a time of deep divisions among some of its members.

Several U.S. and European airlines, including Mr. de Juniac during his tenure at Air France-KLM, have tried to lobby their governments to resist the growth of some of their Mideast rivals, including Emirates Airline and Qatar Airways, whom they accuse of receiving unfair state aid. It is a claim the Persian Gulf airlines have rejected.

At a meeting of the trade group last year in Miami, Qatar Airways Chief Executive Akbar Al-Baker urged the IATA to defend market liberalization. “Any rollback of liberal market access and open skies policies reverberate across the whole world and will lead to retaliatory protectionism,” he said at the meeting.