The action starts in year 9:30 Dragon. No matter what choices have been made during the character creation (gender, race, class, descent), the player meets Grey Warden Duncan and joins the Grey Wardens. Later, he ends up in the south of Ferelden, in the fortress of Ostagar, where people are currently preparing themselves to a battle with the darkspawn, to stop the Plague. The protagonist meets his first companion there - it is Alistair, who is also a Warden. Both of them are sent into the Korcari Wilds to collect samples of darkspawn blood (necessary for the Wardens to prepare joining rituals) and to retrieve scrolls with treaties that the Grey Wardens once used to get help in fighting the Plague from the kingdoms of Thedas. Instead of finding the scrolls, the heroes meet Morrigan, a witch, who invites them to the house of her "mother", a powerful witch Flemeth. After a conversation with her, they obtain the scrolls and return to Ostagar.
Soon, the dusk comes and the army takes its positions. The Warden and Alistair have to make it to the top of a nearby tower and light signal fire, which will mark the beginning of the battle. As they do that, Loghain commits treachery and backs up his forces. King Cailan and Duncan die in the battle, but our heroes are saved by Flemeth. She takes them to her house and allows them to rest there, before they set out on a mission to save the world from the Blight. They intend to use the scrolls to join the dwarves from the Frostback Mountains, the elves from the Brecilian Forest, the mages from the local Circle and the knights of Ferelden in one army (the Arl of Redcliff, Eamon Guerrin, who raised Alistair, helps them to convince the knights). The Warden, Alistair and Morrigan, whom Flemeth commanded to join the team, set out north.
In the meantime, Loghain returns to the capital city, Denerim, and lies about the battle of Ostagar, hiding his treason. Mac Tir outlaws the Grey Wardens and turns back the army that marches to Orlais to help, driven by his distrust towards former occupier. Controversial decision, with Loghain proclaiming himself regent, make the Ferelden aristocracy angry and lead to a civil war.
The heroes arrive at Lothering, which is their first stop on the way from Ostagar. Here, two more people join the team - Leliana, a saintly bard who has given her life to the Maker, and Sten, a Qunari held in a cage for crimes of passion. From this place, the game allows the player to visit various places in any order.
Alistair and Morrigan - two most important team members in Dragon Age: Origin
Let's assume that the player begins his journey from Redcliffe. After arriving there, Alistair reveals that he is a bastard of king Maric (Cailan's father) and has the right to the throne, because all of the descendants are dead. However, he doesn't want to rule over Ferelden. Redcliffe is currently being attacked by demons from the Fade. The cause of that is Connor, son of Arl Eamon. The boy has a wild magic talent, which stayed hidden with the help of his teacher, but now it got out of control and the boy used his powers, desperately trying to heal his father, who has been poisoned by Loghain's people. Having dealt with the demons, our heroes start searching for a cure for Eamon. They head to Denerim, to find Brother Genitivi. As he is currently not in his house, they follow him to the Frostback Mountains. There, they encounter a secret cult and the Urn of Sacred Ashes - a relict, which according to the legend, should contain the remains of Andraste that have healing powers. Using the artifact, the team manages to heal Arl Eamon and get his help. He proposes to call a Landsmeet, to expose Loghain's treachery to the elites of the country.
The Circle of Magi
Let the second destination of the team be the Circle of Magi, which has their quarters in a tower near Lake Calenhad. Problems arise once again, as the building is occupied by abominations (mages using blood magic, who lost control over it) and demons from the Fade. They appeared after Uldred, one of the most powerful mages, attempted treachery with Mac Tir and was exposed. He tried to run, but he was stopped by First Enchanter Irving (the leader of the Circle); a demon summoned by Uldred turned out to be too strong and took control over the tower. On the lower level, the heroes meet Templars, preparing to use the Right of Annulment (killing all of the mages to minimalize the damage that the catastrophe would cause). The team declares that they will solve the problem. They can either kill every mage, following the Templars' instructions, or eliminate only those that deserve it and the monsters. In the second case, Wynne, a respectable mage, joins the team. Depending on the decision that the Warden will make here, either Templars or mages will help him fight the Blight. At the end, it is worth mentioning that one of the characters that the Warden meets in the tower is Cullen, who will play an important role in Dragon Age: Inquisition.
The Brecilian Forest
We move to the Brecilian Forest, home of the Dalish. The problem that the heroes face here are werewolves attack the elves continually. Zathrian, the keeper (leader) of the tribe, sends the team into the wilds, to find a creature called Witherfang and kill it. Obtaining its heart will stop the werewolves attacks and will cure the elves that were bitten. After reaching the center of the forest, the team finds out that the things are a bit different from what the keeper told them. The Warden and his companions meet a mysterious creature called the Lady of the Forest, who tells them that Zathrian is the one responsible for bringing werewolves into the world. Few hundred years ago, he cursed a group of people who attacked his children. After some time, the werewolves started to attack elves, to make the keeper take off the curse. Short after the truth is revealed, Zathrian appears and the Warden has to resolve the conflict. Depending on his decision, either elves or werewolves will help him fight the Blight.
The last stop on the journey for gathering help is Orzammar, the capital of the underground kingdom of dwarves, which once was a network of stone cities (thaigs) connected by the Deep Roads, but now it consists of only one settlement that has to constantly deal with attacks from the darkspawn. The Warden has to resolve a conflict between two pretenders to the throne, after the late king Endrin Aeducan. They are: his son Bhelen (an apt young man, who however killed both his brothers to open his way to the throne) and Lord Pyral Harrowmont (the closest advisor of Endrin and a wise dwarf, whose relatively low descent would be against tradition). No matter who will the Warden choose, the heroes end up in the Deep Roads to search for Branka, a missing female smith who has became a Paragon, and an artifact known as the Anvil of the Void. Completing this task will allow the Warden to learn the mystery of creating golems. Another companion joins the Warden's team - it is Oghren, Branka's husband. After everything is done and the hero decides whether ancient knowledge should or should not be forgotten, the coronation ceremony takes place and the Warden gains the Orzammar's help in fighting the Blight.
Having realized the Grey Wardens treaties, the heroes set out to Denerim, to attend the Landsmeet. Before we speak about that, it is worth mentioning that in the meantime, the team is attacked by elite assassins hired by Loghain, known as the Antivan Crows. During the fight, one of them, elf Zevran, switches sides and joins the Warden. After arriving at his destination, the hero has to gain support of the nobility, before the Landsmeet starts. The most important task is to free Queen Anora, who has been locked by her own father in the dungeon of Arl Rendon Howe's residence, who is the most powerful ally of Loghain. The mission is half successful, as Howe is killed and Anora is rescued, but the Warden and Alistair end up in a cell in Fort Drakon. They free themselves (with or without help from the rest of the team), just in time to make it to the Landsmeet.
The heroes take part in a discussion with the regent, trying to save their good name, to expose Loghain's treachery and to convince the nobility that they should altogether fight against the darskpawn. No matter what they say during the conversation, it ends up in a fight - however, their diplomatic skills will decide whether it will be a bloodbath, or a honorable duel between the Warden and Loghain.
One more problem arises - Grey Warden Riordan, who joins the team in Denerim, reveals that killing the Archdemon will cost the person who strikes the last blow their life. Normally, when an Old God dies, his essences jumps onto the nearest darkspawn, which makes this creature practically immortal, but in a situation when it's a Grey Warden who fights with the Archdemon, the essence is drawn to his body (due to the darkspawn blood, which the Wardens drink during the Joining), which causes the death of both the Old God and the Warden. The same fate would await one of our heroes, if not for Morrigan, who proposes an alternative way. If a Grey Warden (either the main character, if he is a male, or Alistair, or even Loghain) will sleep with her, they will conceive a baby that will absorb the essence of the Archdemon and save the person who kills it.
No matter of whether we agree to the witch's proposal or not, we leave Denerim and set out to face the Archdemon's army. The horde is heading to Redcliffe, which is sort of a meeting point for all the monsters, but after arriving there, it turns out that the Warden's army has been misled. The forces have to go back to the capital, which is currently besieged by the enemy. When both armies fight on the streets of the city, the hero with a few companions makes his way to Fort Drakon, to climb its top and lure the Archdemon to him. We witness the final battle, which ends the Fifth Blight, as well as the plot of Dragon Age: Origins. After the fight, a new ruler of Ferelden is chosen and people start to rebuild their country ruined by the march of the darkspawn.