Act I opens on a muggy autumn afternoon in the garden of Professor Serebryakov's estate. Marina, an old nanny, sits knitting by a samovar as Astrov, the country doctor, paces back and forth. Astrov reminisces about the time when he first came to the region, a time when Vera Petrovna—Serebryakov's first wife and mother to his daughter Sonya—was still alive. Marina notes that since then Astrov has lost his good looks, started to show signs of age, and taken to drinking. Astrov then goes into an extended speech about his "boring, stupid, sordid" life, a life in which he is overworked and surrounded by "eccentric people". As a result, his feelings are "dead to the world": Astrov needs nothing, wants nothing, and loves no one.

Refusing Marina's offer of food, Astrov then recounts how he went to Malitskoe over Lent to treat an epidemic of spotted typhus. One of his patients died while under chloroform, and he is plagued with guilt. Astrov also laments that future generations will not bother to remember those living in the present. Marina comforts him: God will remember.

Voynitsky (or Uncle Vanya), Serebryakov's brother-in-law by his marriage to Vera Petrovna and caretaker of the estate, then enters yawning. He complains that the professor and his wife, having recently relocated to the estate from the city, have thrown the estate out of kilter, drawing everyone into sleep, boredom, and lethargy. Marina concurs, bemoaning the disruption of their dining schedule.

Suddenly Serebryakov,—ridiculously over-dressed in an overcoat, a pair of galoshes, and a pair of gloves—his current young wife Yelena, Sonya, and Telegin, an impoverished landowner dubbed "Waffles" for his pockmarked face, return from a stroll. Speaking of plans to visit a forest preserve, the party enters the house; Telegin joins the group in the garden.

Dreamily Voynitsky sighs about Yelena's beauty. When Astrov reproaches him for not joining the conversation, Voynitsky replies listlessly that he has nothing to say, that he has grown old and lazy. Bitterly, he goes on to caricaturize the other members of the household. His mother, Maria, is a "lazy old crow" who has "one eye fastened on the grave" and the other fixed on her pamphlets "for the dawn of a new life." The professor is an "old, dried up biscuit, a learned, smoke-cured fish", a pompous charlatan of an art historian who knows nothing about art and has already faded into obscurity. Indeed, Serebryakov has spent his life "pouring from one empty pot into the next"—the empty pot of this joke referring to the vacant bodies of his mind, ideas, works, and students.

When Astrov remarks that Voynitsky seems to envy Serebryakov, he readily concurs. In particular, Voynitsky envies Serebryakov's success with women: the examples he adduces are his angelic late sister, his mother (who worships the professor), and the beautiful Yelena. He then points out the illogic of Yelena's fidelity to her dottering, decrepit husband. He questiones how it can be moral to deny one's vitality and youth while immoral to deceive a husband one despises.