Coronavirus disease-2019 (COVID-19) caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) mostly affects the respiratory system but emerging data showed that the human gut is also involved. Microbes in the gut play crucial roles in maintaining immune regulation and metabolic homeostasis. The imbalance of the gut microbiota composition, also known as dysbiosis, has been linked to COVID-19 severity and post-acute COVID-19 syndrome (PACS). In this review, we summarise data from studies published from 2020 to 2021 that have explored the interplay of gut microbiota and COVID-19 susceptibility and severity. We discuss the role of gut microbiota in regulating immunity against SARS-CoV-2 infection and highlight new associations between specific bacteria species and SARS-CoV-2 vaccine efficacy. Therapeutic approaches that target gut dysbiosis in alleviating acute COVID-19 symptoms and preventing PACS are rapidly being developed and tested in clinical trials.