But Lebanon's rival sectarian factions failed to deliver on a commitment to Macron to form a cabinet of specialist ministers by Sept. 15 to start reforms demanded by donors to trigger aid flows.
"It is not yet too late. Everyone must assume their responsibilities and finally act in the sole interest of Lebanon," a French presidency official told Reuters, saying politicians must back the prime minister-designate's efforts.
Mustapha Adib has been seeking to appoint ministers so they can begin work on a French roadmap. Sources say he has sought to switch control of ministries, many of which have been held by the same factions for years.
But major Shi'ite Muslim and Christian players in the sectarian power-sharing system have complained that Adib, a Sunni Muslim, has not been consulting them.
"It appears that some did not understand or did not want to understand that the French initiative is the last opportunity to save Lebanon and to prevent its disappearance," Walid Jumblatt, the leader of Lebanon's Druze community, wrote on Twitter.
He echoed comments by French Foreign Minister Jean-Yves Le Drian, who said last month that Lebanon could disappear without critical reforms.
Simon Abi Ramia, a lawmaker in the Christian Free Patriotic Movement, said on Twitter that Lebanon faced a critical 24 hours in which either the "logic of reason" would win and a government would emerge or Adib would step down.
The French roadmap sets out milestones for a new government, ranging from resuming stalled talks with the International Monetary Fund to fixing the broken electricity system.
But the plan has stumbled at the first hurdle as Lebanon's political elite, who have overseen years of industrial-scale state corruption, have bickered over how the cabinet is formed.
The most significant objections have come from Shi'ite Parliament Speaker Nabih Berri, an ally of Iran-backed Shi'ite group Hezbollah. He has insisted on naming the finance minister, a post he has decided on since 2014.
Hezbollah, a heavily armed group backed by Iran, supports his position, telling President Michel Aoun on Tuesday that Shi'ite ministers must be approved by Shi'ite parties and that the finance minister should be a Shi'ite, sources say.
Former prime minister Saad al-Hariri, a Sunni whose support was critical to Adib's nomination, said no sect had the exclusive right to the Finance Ministry or other portfolios.
In a tweet, Hariri said rejecting the idea of switching control of ministries was frustrating "the last chance to save Lebanon and the Lebanese", referring to the French initiative.
(Writing by Tom Perry; Editing by Edmund Blair and Hugh Lawson) ((email@example.com; Reuters Messaging: firstname.lastname@example.org))