The suspect, an 18-year-old Moroccan asylum seeker, was interrogated on Sunday and is due to appear before a judge early Monday to be remanded in custody, police said.
Four other Moroccan men have also been detained in relation to the attack, however the police have yet to pin down their alleged role in the incident.
The attack happened in the Puutori/Market Square area of Turku just after 4pm local time, with police receiving reports of a man attacking passers-by with a knife.
His alleged crimes are being treated as murder and attempted murder with terrorist intent, a court in Finland said Monday.
An global warrant has been issued for a fifth man who is wanted for questioning, YLE reported.
An 18-year-old Moroccan has been identified as the main attacker in the stabbing rampage in Finland last week. Three were in intensive care, including the main suspect.
The knife attack in western Finland left two people dead and seven others wounded. Among those injured were two Swedes, an Italian and a British paramedic.
Supo says it devotes most of its anti-terrorism resources to tracking the people on the list.
Finnish police said Saturday that the attacker deliberately targeted women.
Both of the women who lost their lives in the attack were Finns, added Granroth. The fugitive in the Barcelona van attack carjacked a man and stabbed him to death Thursday night as he made his getaway, Spanish officials said.
The victims were aged between 15 and 67, according to Granroth.
Prime minister Juha Sipila called for political unity to fast-track already planned legislation giving authorities new powers to monitor citizens online, which he said would reduce Finland's dependence on intelligence from foreign partners.