Varys was born a slave until a sorcerer purchases him. The sorcerer then gave him a potion which rendered him unable to move or speak but did nothing to dull the senses and emasculated him by cutting of both his penis and testes so he could use the organs in a magical ritual burning them in the brazier. No longer having any use for Varys the sorcerer threw him out on the streets to die. Varys resolved to live no matter what and became an excellent thief starting a pick pocket business with Illryio Mopatis.
In order to survive Varys would also sell any use sexual parts remaining to him. Varys eventually found a place on the small council as master of whisperers and utilized a organization of informants who he referred to as Little Birds. Though Varys was manipulative his kindness to the Little Birds was genuine and his ultimate goal was to do what was best for the realm.
Varys Served Aerys Targaryen but when Aerys was overthrown by Robert Baratheon, he received a pardon from Robert. At some point Varys had his servants find the sorcerer gagging him and sending him to Varys in a crate. Varys also worked with Illryio to keep an eye on the heirs of Aerys Viserys and Daenerys, who they hoped to one day put on the iron throne indicating that Varys would have had no problem killing Robert to ensure their ascension.
Varys helped Ned Stark when he was looking into Jon Aryn's murder and implicated Ser Hugh of the vale despite this Ned's daughter Arya later heard Varys and IIIyrio discussing their plans for a dothraki invasion to revive the targaryen dynasty and told her father. However this was of little help to Ned as Arya heard the conversation out of context and without knowing who the speakers were. Varys seemingly supported Robert's proposal to have Daenerys killed but may have been feigning it to hide his true loyalties.
Varys also had a tense confrontation with fellow small council member Littlefinger reminding him that he knew of the illegalities going on in his brothel as well as his framing of Tyrion Lannister for the attempted assassination of Bran Stark, prompting Littlefinger to remind him that he knew of his meeting with Illrryio. When Ned was wrongfully arrested after trying to expose Joffrey Baratheon as a bastard and prove Robert's brother Stannis was the rightful heir to the throne Varys tried talking him into swearing fealty to Joffrey and confess to treason telling him that would save his life in an effort to calm the realm.
While Ned refused at first Varys was able to change his mind by reminding him that defiance could endanger the life of Ned's daughter Sansa. Though Ned did confess Joffrey had him beheaded anyway. Varys was clearly disgusted by the Spectacle and ran to help Sansa when she fainted from shock.
When Varys learned that Tyrion had brought a prostitute called Shae with him to court despite being explicitly told not by his father Lord Tywin Varys approached him and made clear that he had knowledge of his secret angering Tyrion who warned Varys not to threaten him. In spite of their rocky start Varys became an ally to Tyrion helping him install Shae as a handmaiden to a captive Sansa and helping him to plan the defense of King's Landing against Stannis Baratheon (though that was done due to Varys' desire to get revenge on any who used Magic).
When Tyrion was injured in the battle of blackwater Varys sadly told him Tywin was getting all the credit for the victory but assured him that he and many others would never forget the part he played in saving their lives.
Varys then recruited Littlefinger's prostitute Ros, an informer against him. Tyrion sought the help of Varys in uncovering the culprit behind his murder attempt but Varys was unable to help as all he could do was provide whispers. Varys then informed Tyrion of his tragic past and showed him the sorcerer that had been gagged, then advised Tyrion to be patient telling him he would have his revenge if he had the stomach for it.
After a meeting with Ros Varys discovered Littlefinger's obsession with Sansa and plan to smuggle her out of King's landing. He then met with Olenna Tyrell and told her if Littlefinger married Sansa he would take control of the north, something they both agreed would result in chaos. Following this Littlefinger informed Varys he knew of Ros' betrayal and gave her to Joffrey to be murdered, much to his horror.
Varys was present at the wedding of Tyrion and Sansa and could be seen conversing with her. Varys attended the small council meeting where they discussed the murder of Robb Stark among many others at the red wedding.
When Joffrey announced his plan to serve Sansa Robb's head at his wedding to Margery Tyrell. Varys voiced his objection, pointing out that Sansa was now his aunt by marriage. Later that day Varys approached Shae, attempting to bribe her into leaving her due to seeing her as Tyrion's weakness. Shae refused but thought Varys was acting on Tyrion's behalf leading to a strain in their relationship. Varys later told Tyrion that his sister Cersei knew about Shae and intended to tell Tywin urging Tyrion to get her out as soon as possible.
Unable to persuade her of the danger she was in, Tyrion requested Varys lie to save her but he refused. When Tyrion was blamed for Joffrey's murder, Varys testified against him about a threat Tyrion made towards Joffrey when he got angry over Joffrey's comments over his plan to torment Sansa while completely removing the context, though Varys did this in self preservation to avoid incurring Tywin or Cersei's wrath rather than malice toward Tyrion and was genuinely repentant for the betrayal.
After Tyrion was sentenced to death Varys worked with Tyrion's brother Jaime to break him out of prison and save him from execution. In order to keep from being killed himself Varys chose to accompany Tyrion and took him to IIIryio's house. Varys then convinced a reluctant Tyrion to travel to Mereen so he could serve Daenerys eventually. Tyrion forced Varys to let him out of the box he was in for a walk, leading to his abduction by Jorah Mormont.
When Tyrion finally reached Mereen he told Daenerys of Varys' loyalty to her house. When Varys later turned up Tyrion was very happy to be united with him. Varys and Tyrion then traveled through Mereen in disguise in order to locate the sons of The Harpy (a terrorist organization resisting Daenerys's rule). When they learned of the prostitute Vala being in league with the sons of the harpy it was Varys who interrogated her and ensured her co-operation by offering her and her child safe passage on a ship bound for Pentos and a bag of silver to start anew.
Varys later showed signs of disillusionment with Daenerys ad was visibly disturbed when she used her dragons to burn Randyll and Dickon Tarly alive. Varys hid under the crypts during the battle of Winterfell and barely took shelter in an alcove, futilely protecting several of the children. Luck worked in his favor however and he survived over night. Varys noticed the jealousy Daenerys had towards the attention Jon Snow was getting, which he later found out from Tyrion because Jon was Aerys' grandchild and had the better claim to the throne than her.
When Daenerys was prepared to order the destruction of King's Landing, Varys persuaded her to negotiate with Cersei in an attempt to avoid bloodshed. Despite his success Varys had lost all faith in his queen and told Tyrion the more well balanced Jon would make a better ruler than the impulsive and increasingly volatile Daenerys. Varys then sent several letters to various unknown parties telling them of Jon's true parentage. He visited Jon, attempting to convince him he was the right ruler but Jon refused to betray his queen. This exchange was witnessed by Tyrion who reported it to Daenerys. Varys was then burnt alive by Daenerys but before he was, he let Tyrion know that he still considered him a friend and sincerely said he hopped he had been wrong about Daenerys. Sadly Varys' fears were proven true when Daenerys killed many innocent people.