It's March 1960.^[1] Don Draper, a high-level advertising executive at the Sterling Cooper agency in New York City, struggles to find ideas to keep an account for Lucky Strike cigarettes while at the same time managing his tangled personal life; unbeknownst to his stay-at-home wife, Betty, he is having an extramarital affair. Peggy Olson finds employment as Don's new secretary but immediately finds it difficult to fit in with the other secretaries, especially Joan Holloway. Junior accounts manager Pete Campbell, who is about to get married, takes a liking to Peggy and pursues her sexually.

Don continues to conceal his increasingly complicated personal life, even in the face of Roger Sterling's invitation to open up. Meanwhile, Peggy pines for the absent Pete — still on his honeymoon — while fending off the advances of several of the men of Sterling Cooper. Betty's hand-shaking leads her to see a psychiatrist.

Pete returns from his honeymoon, excited about his new marriage, but conflicted about his past encounter with Peggy. Don's business relationship with Rachel develops into a personal attraction. Don and Betty host a birthday party for Sally.

Pete faces pressure from his wife regarding a new apartment. He also further alienates Don and almost loses his job at Sterling Cooper by pitching his own copy to a client in a social setting. However, Bertram Cooper wants him back because of Pete's social connections. Betty meets Helen's ex-husband and babysits her son Glen.

After Don wins an award and has his photo featured in Advertising Age, he must deal with his younger brother coming back into his life. Ken gets a short story published in The Atlantic Monthly, inciting envy amongst his colleagues and driving Pete to ask his wife to meet with an old boyfriend of hers to help him to get published. Peggy overhears a personal conversation on the phone between Don and Midge and shares the secret with Joan.

On Mother's Day morning, Don recalls the birth of his brother, Adam. Roger tries to convince Joan to get her own apartment so they don't have to meet in hotels anymore. At a brainstorming session for Belle Jolie lipstick, Peggy has some interesting ideas that cause Freddie to suggest she be asked to write copy. Rachel faces her conflicting feelings for Don after he seeks out her advice on a new campaign for tourism to Israel.

Roger joins Don for an evening of dinner and drinking, during which Roger makes a pass at Betty, causing a rift in their friendship. The agency prepares for a meeting with members of Nixon's campaign staff. Pete faces trouble at home after he exchanges a wedding gift - a chip and dip - for a rifle. Helen confronts Betty about the night she babysat Glen.

As Peggy's ad copy proves to be successful, her relationship with Pete becomes more complicated. Don spends the evening with Midge and her Bohemian friends. An encounter Don had as a boy with a hobo is told in flashbacks. Sal finds himself the object of interest of a female co-worker and a male client.

McCann Erickson, a larger ad agency, tries to hire Don. They offer Betty a modeling job as a part of their attempt to lure him. Pete devises a strategy to help Nixon's presidential campaign. Peggy's weight gain is noticed in the office. Pete starts a fight after Ken makes an insulting comment about her.

Betty is unhappy about spending the Labor Day weekend with her father's new girlfriend. After Sterling Cooper loses the Dr. Scholl's account, Roger attempts to cheer Don up by arranging for a pair of twins to spend the night with them. This results in Roger having a heart attack. Joan goes out for a night out on the town with her roommate, who reveals her secret love for Joan.

It's October.^[2] Don's brother commits suicide. Peggy's work writing copy for a weight-loss device that is better at providing sexual stimulation earns her a raise. Roger has a second heart attack during a meeting with the head of Lucky Strike. As a result, Don is offered a partnership in Sterling Cooper.

Sterling Cooper's employees have an all-night office party to watch the 1960 Nixon-Kennedy presidential election results.^[3][4] Pete discovers that Don's real name is Dick Whitman, who officially died in the Korean War. When Don tells Pete that Duck Phillips will become the new head of accounts, Pete tries to use this knowledge to pressure Don into giving him the job. Flashbacks reveal how "Dick Whitman" became "Donald Draper".

Betty discovers her friend's husband has been having an affair, leading her to re-evaluate her own marriage. Pete brings in a big account through his father-in-law. Peggy gets promoted to junior copy writer. Also, without realizing she was pregnant, she gives birth. Don learns of his brother's suicide, successfully pitches to Eastman Kodak, and decides not to spend Thanksgiving with Betty's family.