Purpose This trial determines the effect of an Internet-based tailored exercise program compared to usual care control for improving functional capacity and cognition among breast cancer survivors. Methods A two-arm, assessor-blinded, parallel, randomized controlled efficacy trial was conducted. Participants were recruited from the Oncology and Breast unit at the Virgen de las Nieves Hospital (Granada, Spain) between March 2012 to November 2013 and randomized to either the experimental group (an 8-week Internet-based tailored exercise program) or control group (usual care). The outcome measures were the 6-min walk test, Auditory Consonant Trigrams, and Trail Making Test. All were assessed at baseline, post-intervention, and 6-month follow-up. Results After intervention, the telerehabilitation group had significantly improved distances (d = 0.92, P < 0.001) as well as percentage of predicted of the 6-min walk test (d = 0.93, P < 0.001) compared with the control group. Significant improvement was also observed favoring the telerehabilitation group for the number of consonants recalled in total compared with the control group (d = 0.47, P = 0.04). These findings were maintained after 6-month follow-up (d = 0.80, P = 0.001; d = 0.76, P = 0.002; and d = 0.57, P = 0.02, respectively). Analysis was based on intention-to-treat principle. Conclusions These findings support the effectiveness of a telehealth system based on an 8-week physical exercise to achieve improvements and maintain them after 6-month follow-up in terms of functional and cognitive performance in breast cancer survivors. This broad-reach modality could help the growing number of cancer survivors to face their disabling side effects.