Mohammad Chatah, a close adviser to Siniora, was named as finance minister, while Mohammad Fneish, a Hezbollah official, was named as labour minister.
Fawzi Salloukh, a lawyer and diplomat allied to the opposition, was given the post of foreign minister.
The May 21 deal, mediated in Doha, the Qatari capital, ended a poltical stalemate in Lebanon that had given way to the worst fighting since the 1975-90 civil war.
The Doha agreement called for Sleiman to be elected president and a unity government to be formed.
"Our differences will not be resolved overnight, but we have decided to resolve them through institutions and dialogue rather than in the streets," Siniora said.
The cabinet's inaugural meeting is to take place on Wednesday.
Siniora struggled for weeks to form the new unity government in view of intense political wrangling from all sides.
The new unity government sees the opposition take 11 of the 30 cabinet seats.
Hezbollah has one minister, while 10 seats have gone to its allies.
Fouad Siniora remains unchanged from the 2005 cabinet as prime minister, with Issam Abou Jamra, a Greek Orthodox politician, taking up the position of deputy prime minister.
Ziad Baroud is the new interior minister, while Fawzi Salloukh, a Shia who some say is close to Hezbollah, returns to the post of foreign affairs minister.
Mohammad Chatah, a Sunni, is the new finance minister and Ibrahim Najjar is also newly appointed as the justice minister.
Elias Murr stays on as defence minister.
Mohammed Fneish, a Hezbollah supporter, returns to the cabinet as labour minister. He had previously been energy minister until Hezbollah pulled its politicians out of the 2005 cabinet.
Gibran Baassil, the son-in-law of Michel Aoun, the opposition Christian leader, is newly appointed as the telecommunications minister.
Saad al-Hariri, the parliamentary majority leader, said the breakthrough followed a concession by his group to Hezbollah.
"I have asked Prime Minister Fouad Siniora to accept the nomination of Ali Kanso, [the former head of the Syrian Social Nationalist Party]," he said after referring to a figure previously opposed by al-Hariri's camp.
Hezbollah wanted Kanso nominated, but the majority had rejected him because of his party's involvement in the violent clashes in May.
In the new cabinet, Kanso has been made a minister of state.
"People were very frustrated, they saw their political leaders wrangling for weeks and they were sick of them," Al Jazeera's Rula Amin, reporting from Beirut, said.
"But now it [the government] has been formed the challenge is where it goes from here."
Ghassan Ben Jiddou, Al Jazeera's bureau chief in Lebanon, said most of the new ministers were known to be political moderates.
It meant that all political groups have refrained from nominating controversial figures, he said.