Atreus was murdered by his brother, Aegisthus, who took possession of the throne of Mycenae and ruled jointly with his father Thyestes. During this period Menelaus and his brother, Agamemnon took refuge with Tyndareus, king of Sparta, whose daughters Clytemnestra and Helen they respectively married. Helen and Menelaus had one daughter, Hermione.
Menelaus succeeded Tyndareus (whose only sons, Castor and Polydeuces became gods), and Agamemnon, with his brother's assistance, drove out Aegisthus and Thyestes, and recovered his father's kingdom. He extended his dominion by conquest and became the most powerful prince in Greece.
When it was time for Helen, Tyndareus' daughter, to marry, many Greek kings and princes came to seek her hand or sent emissaries to do so on their behalf. Among the contenders were Odysseus, Menestheus, Ajax the great, Patroclus and Idomeneus, but Menelaus was the favorite though, according to some sources, he did not come in person but was represented by his brother Agamemnon. All but Odysseus brought many and rich gifts with them.
Tyndareus would accept none of the gifts, nor would he send any of the suitors away for fear of offending them and giving grounds for a quarrel. Odysseus promised to solve the problem in a satisfactory manner if Tyndareus would support him in his courting of Penelope, the daughter of Icarius. Tyndareus readily agreed and Odysseus proposed that, before the decision was made, all the suitors should swear a most solemn oath to defend the chosen husband against whoever should quarrel with the chosen one. This stratagem succeeded and Helen and Menelaus were married. Following Tyndareus' death, Menelaus became king of Sparta because the only male heirs, Castor and Polydeuces had died and ascended to Mt. Olympus.
Some years later, Paris, a Trojan prince came to Sparta to marry Helen, whom he had been promised by Aphrodite. Helen fell in love with him and left willingly, leaving behind Menelaus and Hermione, their nine-year-old daughter.
Menelaus called upon all the other suitors to fulfill their oaths, thus beginning the Trojan War. Virtually all of Greece took part, either attacking Troy with Menelaus or defending it from them.
During the war, Menelaus' weapon-carrier was Eteoneus. (Odyssey IV, 22, 31.)
After the Greeks won the Trojan War, Helen returned to Sparta with Menelaus (though she had married Paris' brother, Deiphobus, after Paris' death, Menelaus killed Deiphobus). According to some versions, Menelaus stayed in the court of King Polybus of Thebes for a time after the war.
According to one story, after the Trojan War, Menelaus couldn't sail because the wind was calm. He had to catch Proteus, a shape-shifting sea god to find out what sacrifices to which gods he would have to make to guarantee safe passage. Proteus also told Menelaus that he was destined for Elysium (Heaven) after his death.
After Menelaus' death, his illegitimate son Megapenthes, sent Helen into exile.
Here is what Homer's Menelaus had to say about the war and its aftermath after the fact (Odyssey IV):
Menelaus overheard [Telemachus] and said, "No one, my sons, can hold his own with Jove, for his house and everything about him is immortal; but among mortal men- well, there may be another who has as much wealth as I have, or there may not; but at all events I have travelled much and have undergone much hardship, for it was nearly eight years before I could get home with my fleet. I went to Cyprus, Phoenicia and the Egyptians; I went also to the Ethiopians, the Sidonians, and the Erembians, and to Libya where the lambs have horns as soon as they are born, and the sheep lamb down three times a year. Every one in that country, whether master or man, has plenty of cheese, meat, and good milk, for the ewes yield all the year round. But while I was travelling and getting great riches among these people, my brother was secretly and shockingly murdered through the perfidy of his wicked wife, so that I have no pleasure in being lord of all this wealth. Whoever your parents may be they must have told you about all this, and of my heavy loss in the ruin of a stately mansion fully and magnificently furnished. Would that I had only a third of what I now have so that I had stayed at home, and all those were living who perished on the plain of Troy, far from Argos. I often grieve, as I sit here in my house, for one and all of them."
See also: