The two-day meeting is being hosted by the Turkish government, which has tried to raise Turkey’s profile in Somalia since last year’s drought there.
Traditional elders, business leaders and civil society groups from Somalia are also due to attend.
They are expected to discuss the end of the transition period of the UN-backed interim government, due in August.
The agenda for the conference is similar to that of numerous big meetings on Somalia in recent times, the BBC’s Mary Harper reports.
But Turkey has had more success than other countries in actually bringing about change on the ground, she adds.
During last year’s famine in Somalia, Turkish Prime Minister Recep Tayyip Erdogan and his wife went to the Somali capital, Mogadishu – the first visit by a leader from outside Africa for nearly 20 years.
Turkey has since been at the forefront of helping build roads, schools and hospitals there.
However, some Somali politicians have said Turkey has not been transparent about the conference, failing to consult them about who to invite, our correspondent says.
Last week, leaders of disparate Somali factions agreed to a timetable that will elect a new president by 20 August.
The conference will discuss how the country will function after the end of that transitional period and will try to agree a common international policy towards Somalia.
Economic issues such as energy, water and roads will also be on the table.
However, representatives from the semi-autonomous Puntland region in the north have reportedly said they will not be attending.
Earlier this week, the convoy of Somali President Sheikh Sharif Sheikh Ahmed came under attack from the Islamist militants of al-Shabaab, after he made a visit to the newly captured town of Afgoye.
The president escaped unharmed but at least one Somali government soldier was killed and four were wounded in the attack.
The country has been without an effective central government since 1991 and has been racked by fighting ever since – a situation that has allowed piracy and lawlessness to flourish.