The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is an emergent infectious pathogen causing an acute respiratory disease called corona virus disease 2019 (COVID-19). Virus transmission may occur by contact, droplet, airborne or via contaminated surfaces. In efforts to effectively control the COVID-19 outbreak, the world health organization (WHO) and the Saudi Ministry of Health (MOH) have advised the public to practice protective measures to reduce transmission of the virus and reduce incidence of infection. These measures include hand washing, wearing masks and gloves and avoidance of touching the face with unwashed hands. The current study aimed to investigate knowledge and adherence of the Saudi population to these protective actions during the pandemic. After determining the required sample size using power analysis, a cross-sectional online self-reported survey of 5105 Saudi residents was conducted between 25th March to 17th April 2020 to evaluate public knowledge of COVID-19. Participants were all aged 18 years or above, Arabic speakers and residents of Saudi Arabia. Scores were calculated based on knowledge and adherence of the individuals to protective measures. About 90% of participants exhibited a high level of knowledge (scored 2/2) and practice (scored > 3/6) in relation to hand hygiene and wearing gloves and masks. Practice scores were positively associated with females and individuals with high income. Lower practice scores were linked to youth and residents of the northern and western regions of the Kingdom. Over two thirds of participants preferred hand washing to alcohol disinfection, and the frequency and performance of hand washing improved during the pandemic for more than half of respondents. Overall, the findings reflected high public knowledge of SARS-CoV2 transmission routes and adherence to personal protective measures. However, public awareness campaigns with an emphasis on the youth and individuals with low education and income are required to improve overall practice.