From Legion Wiki
- Rokk Krinn, Imra Ardeen, and Garth Ranzz save R.J. Brande from an assassination attempt at Metropolis Space Port. Mr. Brande convinces the three youths to form the Legion of Super-Heroes as Cosmic Boy, Saturn Girl and Lightning Lad respectively.
- Cosmic Boy becomes the Legions first leader.
- Triplicate Girl and Phantom Girl join.
- Chameleon Boy, Colossal Boy, and Invisible Kid (Lyle Norg) join.
- Supergirl and Brainiac 5 join.
- Superboy joins.
- Cosmic Boy is re-elected leader.
- Ultra Boy joins.
- Star Boy joins.
- Shrinking Violet and Sun Boy join.
- Bouncing Boy joins.
- Mon-El is briefly freed from the Phantom Zone to assist the Legion, and is given Honorary Membership.
- Matter-Eater Lad joins.
- Saturn Girl is elected Leader.
- Lightning Lad is killed repelling Zaryan the Conqueror.
- Mon-El is permanently freed from the Phantom Zone when a cure is found for his lead poisoning. He becomes a full member.
- The Legion of Substitute Heroes is formed by 5 rejected applicants - Chlorophyll Kid, Fire Lad, Night Girl, Polar Boy and Stone Boy.
- Element Lad Joins.
- Lightning Lass joins.
- Proty I sacrifices it's life in order to resurrect Lightning Lad.
- Dream Girl joins.
- Dream Girl transforms Lightning Lass' power from electricity to gravity nullification, turning her into Light Lass. Dream Girl resigns shortly after, some time after she joins the Legion of Substitute Heroes.
- Bouncing Boy loses his power and resigns. He is given honorary status.
- Saturn Girl is re-elected Leader.
- Lightning Lad loses his right arm while battling the Dxaundii, Moby Dick of Space.
- Brainiac 5 is elected leader.
- Brainiac 5 creates Computo, which quickly attempts to conquer the Earth. One of Triplicate Girl's bodies is killed, and she becomes Duo Damsel.
- The Legion creates the position of Deputy-Leader, which Saturn Girl is elected to, in the wake of the Computo Crisis.
- Star Boy kills in self-defence, a violation of the Legion Code, and is expelled. He joins the Legion of Substitute Heroes.
- Ferro Lad, Karate Kid, Nemesis Kid, and Princess Projectra join.
- The Legion helps to repel a Khundian Invasion. Nemesis Kid is revealed to be a traitor, but escapes.
- Invisible Kid is elected Leader, with Superboy as Deputy.
- Star Boy, Dream Girl, and Bouncing Boy are readmitted.
- Lightning Lad's arm is regrown.
- With the approach of the Sun-Eater, the Legion is dangerously under powered, so they recruit criminals in an attempt to destroy the creature. Tharok, Mano, Emerald Empress, the Persuader, and Validus form the Fatal Five.
- Ferro Lad is killed while destroying the Sun-Eater.
- Shadow Lass joins.
- Legion Academy opens.
- The Legion adopts 6 month terms for Leaders and Deputy-Leaders.
- Ultra Boy is elected leader, Mon-El is deputy.
- Chemical King and Timber Wolf join, after infiltrating the Legion of Super Villains.
- Karate Kid is elected leader, Mon-El is deputy.
- Mon-El is elected Leader, Element Lad is deputy.
- Ultra Boy is elected Leader. The Legion experiments with rotating deputy leaders.
- Timber Wolf is declared dead after an explosion on Asteroid X-52.
- Full year terms are reinstated, and the rotating deputy's are dropped.
- Mon-El is elected Leader, Sun Boy is deputy.
- Timber Wolf returns.
- Bouncing Boy and Duo Damsel get married and resign. (The Legion Constitution prohibits married members).
- Wildfire joins.
- Invisible Kid is killed by Validus.
- Matter-Eater Lad resigns after he is drafted into politics on his homeworld.
- Tyroc joins.
- Wildfire is elected Leader, Element Lad is Deputy.
- Dawnstar joins.
- Chemical King is killed thwarting the Dark Circle's plan to plunge the Earth into World War VII.
- Lightning Lad and Saturn Girl get married and resign.
- The Earthwar is waged. In the aftermath the constitution is amended allowing for married couples. Lightning Lad and Saturn Girl rejoin. Bouncing Boy and Duo Damsel become reserve members.
- Lightning Lad is elected Leader, Element Lad is deputy.
- Brainiac 5 goes insane, creating the destructive Omega creature. Matter-Eater Lad is also driven insane after he consumes the Miracle Machine.
- The League of Super Assassins make their first assault on the Legion. They are defeated by the Legion of Substitute Heroes.
- Brainiac 5 recovers.
- Tyroc resigns.
- Blok joins.
- Brainiac 5 accidentally revives the Computo matrix. Jacques Foccart uses Lyle Norg's formula to defeat Computo, and takes his codename to join the Legion as Invisible Kid.
- Matter-Eater Lad is cured.
- Shrinking Violet is secretly kidnapped by Imsk radicals. They dupe the Durlan actress Yera into replacing her.
- Princess Projectra becomes Queen Projectra upon the death of her father. She and Karate Kid become reserve members when she returns to her home world to take the throne, Karate Kid as her consort.
- Dream Girl is elected Leader, Element Lad is deputy.
- Darkseid attempts to conquer the galaxy, but is fought to a stand still by the combined might of the Legion, Legion of Subs, Wanderers, Heroes of Lallor, and Legion Reserve. Element Lad resigns as Deputy Leader.
- Ultra Boy becomes deputy, but quits shortly after.
- White Witch joins.
- Light Lass resigns and returns to Winath.
- Star Boy becomes deputy.
- Colossal Boy and Shrinking Violet (Yera) secretly wed. Once the truth of Yera's identity is revealed they agree to continue the marriage.
- Shrinking Violet is rescued.
- Karate Kid and Queen Projectra get married.
- Element Lad is elected Leader. Dream Girl is deputy leader.
- Saturn Girl gives birth to Graym and Garridan Ranzz.
- Karate Kid is killed in the Legion of Super-Villains attack on Orando. Queen Projectra kills Nemesis Kid.
- Light Lass rejoins the group as Lightning Lass.
- Cosmic Boy, Saturn Girl, and Lightning Lad resign to take advisory roles.
- It is around this point in the time line when the events of the Crisis on Infinite Earths begin to affect the Legion.
- This timeline is based on the tenure of the Legion leader, who was elected to serve a one-year term. Regardless of publication history, all events occurring between leadership elections are considered to have happened in one Earth-standard calendar year. The six-month terms in years 7 and 8 is the generally accepted (though non-canonical) duration due to the team's publication status at the time.