Lewis Ludlow, a converted Muslim, pleaded guilty to funding the Daesh abroad as well, according to the Sky News broadcaster.
In May, the young man told Westminster Magistrates' Court he was innocent of researching and planning attacks in London.
The UK has been hit by numerous terror attacks over the past few years, with several young Muslims being radicalized online by Daesh-linked extremists.
Last year, three assailants killed eight civilians in central London, in addition to injuring almost 50 bystanders in their Daesh-inspired attack. Another attack, this time a suicide bombing at a concert in the city of Manchester, left dozens dead and injured.
*Daesh (also known as ISIS/ISIL/IS) is a terrorist group banned in Russia