The first season of the television series Angel, the spin-off of Buffy the Vampire Slayer, premiered on October 5, 1999 on The WB Television Network and concluded its 22-episode season on May 23, 2000. The season aired on Tuesdays at 9:00 pm ET, following Buffy.

If you need help, then look no further. Angel Investigations is the best. Our rats are low... (What? It says "rats." Sorry.) Ahem... our rates are low, but our standards are high. When the chips are down, and you're at the end of your rope you need someone that you can count on. And that's what you'll find here -- someone that will go all the way, no matter what. So don't lose hope. Come on over to our offices and you'll see that there's still heroes in this world." For over two centuries, Angelus was one of the most vicious vampires ever to walk the earth. Then he killed the wrong girl, and her grieving Gypsy family cursed the vampire with the return of his soul, causing him to suffer with remorse for all the hundreds of innocents that he had killed through the years. Now he goes by the name Angel, and he fights to protect the helpless from those who would prey upon them as he himself once did. After three years of living in Sunnydale, fighting alongside his girlfriend Buffy, Angel has moved to Los Angeles to continue the good fight. Aided by a few old friends and some new ones, Angel must take on vampires, demons, lawyers, and all of the other dark forces that Los Angeles has to offer.

The vampire Angel, cursed with a soul, moves to Los Angeles and aids people with supernatural-related problems while questing for his own redemption.

At the end of the third season of Buffy, the 242 year old, re-ensouled vampire Angel left Sunnydale to give teenage Slayer Buffy Summers the chance to live a normal life. Angel is now living in the big city of Los Angeles. With Buffy gone Angel is now completely cut off from society, every day getting closer and closer to giving in to his vampiric hunger. It's not until he befriends the half demon Doyle, who is sent visions of people in trouble by The Powers That Be, and fellow Sunnydale resident Cordelia Chase, who grounds Angel's life in the humanity around him, that he truly begins to take charge of his life and seek atonement for his past sins. He sets up his own detective agency, Angel Investigations and begins to "help the helpless". Early in the season, Angel befriends a female detective named Kate Lockley who at first helps and befriends Angel but turns on him after she finds out what he truly is. As the season comes to a close, Angel gains a semi-ally in the form of street smart, vampire hunter named Charles Gunn who will officially join the team early in the next season. Throughout the year Angel and co. are frequently set upon by the demonic law firm Wolfram & Hart, and the antics of two up and coming lawyers Lindsey McDonald and Lilah Morgan, who have secret plans concerning the vampire with a soul and the role he plays in the forthcoming apocalypse.

In "I Will Remember You" Buffy comes to L.A. during which Angel is cured of his vampirism by the blood of a Mohra demon. He and Buffy then share the perfect day they always dreamed of together. However, Angel asks the Oracles to reverse time so that he can continue to help people in need realizing that he cannot protect the world as a normal human man. He subsequently gives up the one thing he ever truly loved to continue fighting the good fight. A few days later Doyle sacrifices his life as an act of redemption when he saves the lives of a family of half demon refugees. Before he dies he gives Cordelia a long awaited kiss as the two had slowly been building a relationship all year and passes the godly visions on to her. In his place, ex-watcher Wesley Wyndam-Pryce arrives and aids the team with his extensive knowledge of demonology and the occult. In the two-parter, "Five by Five" and "Sanctuary", the rogue Slayer, Faith shows up in L.A. and is contracted by Wolfram & Hart to kill Angel. After torturing Wesley she ends up breaking down in Angel's arms, screaming at him to kill her. She eventually admits to the many crimes she has committed and hands herself in to the police. Seeing someone else so willingly seek redemption allows Angel to re-affirm his role and to willingly cut himself off from Buffy. During the season finale Angel comes across an ancient prophecy that concerns his fate. Wolfram & Hart summon the demon Vocah to "destroy all avenues to the Powers That Be" and summon forth an ancient, terrible evil; Angel's sire, Darla the vampire. Wesley finishes translating the prophecy and learns that the word Shanshu means to both live and die informing Angel that if he truly saves the world he will be made human again and his burdens will be forever lifted. Meanwhile, the Angel Investigations offices are blown up forcing the gang to work out of Cordelia's apartment who, after having seen all the pain that infests Los Angeles, has vowed to up her stance in the fight against evil and become a better person.