As a young woman, Goodall was interested in African animals; she was able to move to Kenya after finding work as a secretary to Dr Louis Leakey, an eminent archaeologist and palaeontologist. After Leakey obtained the approval of his co-researcher and wife, paleoanthropologist Mary Leakey, he laid out his plans to Goodall; he believed that the study of existing great apes could provide clues to the behaviour of early hominids and was looking for a chimpanzee researcher.

Leakey sent Goodall back to Britain to study primate behaviour and anatomy, and in 1960 he acquired the funds to allow Goodall to begin a research project at the Gombe Stream National Park in Tanzania. Thus, Goodall became the first of three women, later known as "The Trimates" (or "Leaky's Angels"), chosen by Leaky to study great apes (alongside Dian Fossey, who studied gorillas, and Birutė Galdikas, who studied orangutans). In 1962, Leaky sent Goodall to the University of Cambridge, where she became the eighth person to be allowed to complete a PhD there without first having obtained a BA or BSc degree. Her thesis, which was based on the first five years of her research at Gombe Stream, was completed in 1966 under the supervision of Professor Robert Hinde.

Goodall's research is well known within the scientific community for challenging two long-standing beliefs held at the time: firstly, that only humans had the capacity to construct and use tools; and secondly, that chimpanzees were exclusively herbivores/insectivores. When observing the Kasakela chimpanzee community at Gombe Stream, she noted that some chimpanzees would stick long blades of grass into termite holes, then remove them when covered with termites, effectively "fishing" for the insects. Goodall also discovered that chimpanzees regularly hunt smaller species of primates such as colobus monkeys and share the carcass among the troop. Years of observation led Goodall to identify violence within chimpanzee communities, including the deliberate killing of other females' young by the troop's dominant females in order to maintain their place in the troop hierarchy.

Of course, one of Goodall's most significant feats is her acceptance into chimpanzee society. After many months of long-distance study, the Kasakela chimpanzee community gradually began to adjust to Goodall's presence – rather than fleeing when she was within 500 yards of the group, they allowed her to watch them from a distance of 100 yards. She began the long process of being able to recognise individual troop members and learned the basic behaviour patterns of the group. It was during this stage that Goodall started recording how members of the troop communicated with each other – both through body language and vocalisations. The fear towards her reportedly turned to curiosity, then to defiance at her intrusion. After a year, her arrival was greeted with excitement or indifference. At one watershed moment, a new member of the troop (whom she named "David") took bananas that Goodall brought from her camp and ate them; thereafter, he would accept bananas from Goodall and would sit with her as he ate them. This proved to be Goodall's entry point into the Kasakela troop – David eventually brought other members of the troop to share the bananas, and soon a trio of chimpanzees was stealing pieces of cloth from Goodall's camp! For a period of 22 months, Goodall was the lowest-ranking member of the troop. She would groom and be groomed by other members, and she would communicate with them in a rudimentary fashion by mimicking their calls and gestures.

Goodall credits the 1986 Understanding Chimpanzees conference at the Chicago Academy of Sciences with shifting her focus from chimpanzee observation to a broader interest in conservation. In recent years, Goodall has focused on her writing, which has produced several international bestsellers, a number of educational initiatives and a career as a conservationist. She received a knighthood from Queen Elizabeth II in 2004 for her dedicated and ground-breaking research, as well as for her conservation efforts and wider activism.

Regarded as a global leader in the effort to protect chimpanzees and their habitats, Goodall has founded a number of conservation projects in Africa. These include the Tchimpounga Chimpanzee Rehabilitation Center in the Republic of Congo, which cares for orphans of the bushmeat trade, and the Lake Tanganyika Catchment Reforestation and Education project, which protects chimpanzee territory around the Gombe Stream through reforestation and the education of local communities on sustainability.

Goodall is also a committed vegetarian; she advocates the diet on the basis that it is ethical, healthy and good for the environment. She is an outspoken proponent of farm animal welfare, criticising industrial farming techniques that she believes are painful, degrading and inhumane as well as extremely harmful to the environment. Her opposition to hunting animals for sport and the use of animals for medical experimentation is also notable, although she has attracted criticism for her views of the latter from scientific experts who contend that ethical animal experimentation is a crucial part of lifesaving research.

To date, Goodall continues to work alongside several conservation and animal welfare organisations, including the Nonhuman Rights Project, Advocates for Animals and Population Matters. She was named a United Nations Messenger of Peace by Secretary-General Kofi Annan in 2004, and is an honorary member of the World Future Council. In 2020, Goodall vowed to plant five million trees as part of the World Economic Forum's one trillion tree initiative and in February 2021 she, along with over 140 scientists, called on the EU Commission to ban the caging of farm animals. At present, Goodall devotes virtually all of her time to advocacy on behalf of chimpanzees and conservation of the environment, travelling nearly 300 days a year.