Human:

Archer: immediately availible
Black Mage: immediately availible
Soldier: immediately availible
Thief: immediately availible
White Mage: immediately availible
---
Fighter: requires 2 Soldier skills learned before its availible
Hunter: requires 2 Archer skills learned before its availible
Ninja: requires 2 Thief skills learned before its availible
Paladin: requires 2 Soldier skills learned before its availible
Blue Mage: requires 1 Black Mage skill and 1 White Mage skill learned before its availible
Illusionist: requires 5 Black Mage skills and 3 White Mage skills learned before its availible

Viera:

Archer: immediately availible
Fencer: immediately availible
White Mage: immediately availible
---
Elementalist: requires 1 Fencer skill and 1 White Mage skill learned before its availible
Red Mage: requires 1 Fencer skill learned before its availible
Sniper: requires 2 Archer skills learned before its availible
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Assassin: requires 1 Sniper skill and 2 Elementalist skills learned before its availible
Summoner: requires 2 White Mage skills and 2 Elementalist skills learned before its availible

Moogles:

Animist: immediately availible
Black Mage: immediately availible
Thief: immediately availible
---
Gunner: requires 1 Animist skill learned before its availible
Mog Knight: requires 1 Animist skill learned before its availible
Gadgeteer: requires 2 Thief skills learned before its availible
Juggler: requires 2 Thief skills learned before its availible
Time Mage: requires 5 Black Mage skills learned before its availible

Nu Mou:

Beastmaster: immediately availible
White Mage: immediately availible
Black Mage: immediately availible
---
Morpher: requires 5 Beastmaster skills learned before its availible
Sage: requires 2 Beastmaster skills and 3 White Mage skills learned before its availible
Illusionist: requires 3 White Mage skills and 5 Black Mage skills learned before its availible
Alchemist: requires 3 White Mage skills and 5 Black Mage skills learned before its availible
Time Mage: requires 5 Black Mage skills learned before its availible

Bangaa:

Warrior: immediately availible
White Monk: immediately availible
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Dragoon: requires 2 Warrior skills learned before its availible
Defender: requires 2 Warrior skills learned before its availible
Gladiator: requires 2 Warrior skills learned before its availible
Bishop: requires 2 White Monk skills learned before its availible
Templar: requires 2 White Monk skills learned before its availible

Article Source: Kuponut.com : Final Fantasy Tactics Advanced Class Chart  :  http://www.kuponut.com/cheats/ffta/class_chart.html