The firm also pegged global mobile phone users to reach 4.55 billion in 2014.
"The global smartphone audience surpassed the 1 billion mark in 2012 and will total 1.75 billion in 2014. eMarketer expects smartphone adoption to continue on a fast-paced trajectory through 2017," the firm said.
Nearly two-fifths of all mobile phone users, close to one-quarter of the worldwide population, will use a smartphone at least monthly this year, it added.
The firm said the slowing mobile adoption will get a boost from developing regions in Asia-Pacific and other places.
"eMarketer expects 4.55 billion people worldwide to use a mobile phone in 2014. Mobile adoption is slowing, but new users in the developing regions of Asia-Pacific and the Middle East and Africa will drive further increases," it added.
Between 2013 and 2017, mobile phone penetration will rise from 61.1 per cent to 69.4 per cent of the global population, the research firm said in its 'Worldwide Mobile Phone Users: H1 2014 Forecast and Comparative Estimates' report.
Mobile phone users are fast switching over to smartphones as devices become more affordable and 3G and 4G networks advance, it added.
"More than 2.23 billion people worldwide, 48.9 per cent of mobile phone users, will go online via mobile at least monthly in 2014 and over half of the mobile audience will use the mobile Internet next year," eMarketer said.
Analysts feel that mobile data network expansion in emerging markets with a rising middle class and the adoption of smartphones and feature phones with Internet capabilities will fuel the growth of mobile Internet.
Rising low-cost smartphone devices with dual core processors and multi GB RAM being offered by many smartphone vendors will also lead to greater data consumption and a growth in communication over smart devices.
In 2014, mobile devices will become the primary computing devices for many end users and smartphone users will seek full-functionality and access to major applications and data from their mobile devices.