Breast cancer (BC) and its treatments decrease patients' psychological well-being. Peer support is one form of social support, but little is known about what gives rise to peer support. The purpose of this study was to examine how peer support is constructed among recently diagnosed BC patients. Eighteen women were randomly picked from 130 women who had received phone calls from a trained peer supporter and were invited to group interviews. In the interviews, patients discussed their cancer, peer support experiences, and social support. The transcribed data were analyzed using Braun and Clarke's thematic analysis approach. The construction of peer support among newly diagnosed BC patients was complex. It depended on the needs of the patient and the success of interactions. Once they had received a diagnosis, the lives of the patients changed suddenly, and patients dove into the I-we-others consideration and had a need to talk. Interaction with peer supporters gave them a chance to share their stories. At their best, interactions led to belonging, caring, and a sense of security. The need to be heard and seen is strong in a patient's changing health situation. Peer support plays an important role in high-standard care and in strengthening patients' self-determination. Hospitals should create chances for supportive communication, and the supportive communication should be easily accessible and successful. The training of peer supporters should ensure that they have reflected on their own BC process and know how to consider the needs of newly diagnosed patients.