Juno is Hera's Roman counterpart. While the Greeks envisioned Hera as imperious and proud, the Romans saw her counterpart as the patron goddess of Rome. As Juno, she becomes more disciplined, militaristic, and warlike.

Some time before the start of the series, Juno learned of the seven demigods who would be needed to battle the forces of Gaea by the Fates. In response, she started working behind Jupiter's back and began to prepare them for the coming battle.

She appeared to a child of Mars named Frank Zhang and told his mother Emily Zhang, that his life force was tied to one of the sticks in the fire, and once it burned up, he would die. Frank's grandmother quickly took the burned piece of wood from the fire, and Emily kept it until she went to war in Afghanistan, upon which Emily gave it to Grandma Zhang to give to Frank if she did not come back. After Emily's death, Frank brought the stick with him to Camp Jupiter.

After the Second Titan War, she came up with a plan to make Camp Half-Blood and Camp Jupiter work together. However she was captured by Gaeawith the help of the snow goddess Khione, and Gaea began to drain Juno's power to raise Porphyrion. Juno managed to save up enough energy to send Jason Grace to Piper McLean and Leo Valdez, where he would be taken to Camp Half-Blood. A few days earlier, she had also transported Percy Jackson away from Camp Half-Blood and put him to sleep until the time was right.