He was speaking on Thursday at an event in the Committee of the Regions in Brussels on efforts to tackle radicalisation.
De Kerchove said that understanding of radicalisation and what drives young Muslims to join groups like Isis has changed.
He said, "In the past, we thought it was a long process and that radicalisation couldn't take place simply online, but now we are seeing teenagers being radicalised on the internet and leaving for Syria after just 15 days."
In a speech, he emphasised the role of criminality in the process, saying, "If we look at the perpetrators of Paris and Brussels, most of them have a criminal past."
He also said that, "perhaps the most interesting part of the Commission's [recent] communications" is that "we need to mainstream counter-violence extremism in many policies, not to be driven by it."
De Kerchove also said that the role of local and regional authorities is "critical", saying that this is the "most relevant area" for prevention work.
When it comes to prevention and mainstreaming counter-violence efforts, he said it was necessary to "think big, out of the box".
He cited, as an example, the fact that he had just met the director of the opera in Brussels, who "has launched an opera" by recruiting 250 youngsters from neighbourhoods unfamiliar with opera, giving them six months training in singing and, in effect, taking them into "a new world".
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Another example was from the US, where President Barack Obama had launched the so called Stevens Virtual Exchange Programme, meant to connect one million Arabs and Americans to have educational classes online.
He went one to liken this to the Erasmus programme, saying, "We know how much Erasmus removes stereotypes; we need to do more of the same."
He said that he believes the most urgent thing is "to handle the huge number of foreign fighters who will come back because we are winning in Syria and Iraq."
He added, "I would predict that Isis will be completely defeated in a year."
Turning to current issues surrounding refugees and migration, he said the international community should "be extremely vigilant."
There is a "need to develop a European Islam", he said, while adding that the role of ideology in radicalisation is complex.
"We know that ideology may play a role. We need to develop an environment in which Islam develops in Europe in the same way as other religions."
Speaking in the same debate, Karl Vanlouwe, a member of the Flemish Parliament, said, "Looking away from the problem is something that must be put into the past. We need to go on the offensive in defence of our European value. For too long we have averted our gaze from this problem. We need to defend European society against this ideology."
"In the Flemish government we have a 100-point programme. We need to get family and friends on board. One specific measure that is very important is deradicalisation in prison."
At the meeting, the CoR formally adopted an opinion drafted by Bart Somers, mayor of Mechelen in Belguim, which has an unusually large percentage of young Muslims in its population although no one from the town is known to have gone to Syria or Iraq.
It was for that reason the CoR asked Somers to write a report on countering radicalisation and violent extremism.
De Kerchove described it as "an extremely good report" and "very comprehensive" with "many interesting ideas".