Agamemnon puts Odysseus in charge of the expedition to bring Chryseis back to her father.
Later, when Agamemnon's loyalty-test backfires and all the Achaians start running for their ships, Athene tells Odysseus to intervene and put things right.
First he borrows Agamemnon's scepter, as a sign of authority. Then he goes among the soldiers; whenever he sees a soldier of high rank, he asks him politely not to run away. Whenever he sees a soldier of lower rank, he gives him the same message – by hitting him with the scepter!
When the Achaians come back to the assembly, one rabble-rouser, Thersites, keeps insulting Agamemnon and saying they should sail home.
Odysseus intervenes, tells Thersites off, and then beats him up with Agamemnon's scepter. The other soldiers cheer.
Now is the moment for Odysseus to follow this up with an inspiring speech. He reminds them of something that happened nine years earlier. At the time, they received a sign from the gods that the seer Kalchas interpreted to mean that they would take Troy in the ninth year of the war.
Later on, in Book 3, while Helen and the fogeys of Troy are watching the troops assemble on the plain, Antenor reminisces about a time earlier in the war when Menelaos and Odysseus came to Troy together to ask for Helen back. He says that everyone was impressed with Menelaos's physique but that Odysseus's speaking ability knocked everyone's sandals off.
A little later, after the duel between Menelaos and Paris gets messed up, Menelaos gets shot by Pandaros, and the battle is about to begin, Agamemnon comes upon Odysseus and some other guys who are chilling out at the back of the army. (They're so far back that they haven't even heard the order to attack yet.)
Agamemnon insults Odysseus and says, "What's the deal? You're always first in line when you're coming to one of my feasts. How come you're hanging back now?"
Odysseus tells him to back off, and not pass judgment until he sees him fighting.
Odysseus fights bravely in the battle.
Later on, when Hektor challenges the Achaians to a one-on-one duel, after some prodding from Nestor, Odysseus is one of those who cast lots to accept the challenge – along with Agamemnon, Diomedes, Aias, and little Aias. Aias is picked.
As we know, this duel ends in a truce. Two days later, after both sides have buried their dead and the Achaians have built their wall, the battle starts again.
At one point, the Achaians are put to flight. Diomedes sees Odysseus running away and calls out to stop him. Odysseus doesn't listen and keeps on running.
That night, Odysseus is part of the unsuccessful delegation to entice Achilleus back to the fight.
Later that same night, Diomedes picks Odysseus to accompany him on a reconnaissance mission into no-man's-land.
During their raid, they capture Dolon, a Trojan spy. After finding out the layout of the Trojan camp – and the location of King Rhesos's horses – Diomedes beheads him.
Odysseus and Diomedes now make their way into the Trojan camp, where they find the sleeping King Rhesos and his men, just as Dolon described.
While Odysseus unhitches the horses, Diomedes murders the lot of them in their sleep.
Then the two Achaians make a quick getaway, with the horses, back to their camp. They stop en route to pick up the fancy armor Diomedes stripped from Dolon.
When they get back to base, they offer prayers of thanks to Athene.
The next day, in battle, Odysseus teams up with Diomedes again to put a stop to Hektor's rampage. This results in Diomedes briefly knocking Hektor unconscious with his spear.
Eventually, though, both Diomedes and Odysseus get injured and withdraw from the fighting.
Behind the lines, they confer with other wounded leaders, where Odysseus convinces Agamemnon not to start sailing away for home. He argues that as soon as the men see them sailing off, they won't keep fighting and will all be killed.
The next day, after the death of Patroklos and the rearmament of Achilleus, Odysseus makes the sensible case that the soldiers have to eat breakfast before they fight.
Then Odysseus insists – even though Achilleus doesn't appear to care that much – that Agamemnon give Achilleus the gifts he promised. Odysseus arranges the presentation of the gifts.
Later on, during the funeral games for Patroklos, Odysseus competes in a wrestling match against Aias. They are starting on their third round when Achilleus declares a draw. He tells them to share the prizes (we are not told how).
Then Odysseus wins a footrace with the help of Athene, who makes Aias slip in cow dung.