Consumers will spend 800 hours on mobile internet this year, increasing to 930 hours by 2021 to account for 31% of global media consumption in that year, up from 27% in 2019.
The amount of time spent reading newspapers, viewing TV and using desktop internet has fallen between 2014 and 2019, Zenith's latest Media Consumption Forcasts report shows.
However, the growth of mobile internet is slowing as most people in developed countries now have a mobile device and mobile phone ownership has become more common in developing markets.
The study, which examines the amount of time people spend across various media and how this will change betweem 2019 and 2021, added that total media consumption has risen to eight hours a day, up from seven hours in 2013. This is expected to rise to eight-and-a-quarter hours by 2021.
It also explained that TV is the biggest medium globally, with viewing only expected to dip slightly. TV will account for 33% of all media consumption in 2021, down from 35% in 2019.
Radio and cinema, meanwhile, remain attractive, with radio listening rising from 53 minutes to 55 minutes and time spent at the cinema rising from 1.8 minutes to three minutes a day on average. Zenith said this is down to a boom in cinema attendance in China.
Jonathan Barnard, head of forecasting at Zenith, said: "Mobile internet technology has expanded both the amount of time people spend with media and what counts as media. [It] now means comparing prices on the high street, sharing jokes with friends and booking your next holiday, opening up new opportunities for brands to connect with consumers."