Ireland is hosting the tournament from May 3-19 across seven different venues and O'Brien's Under-17 squad would certainly benefit from a strong home crowd when they take on Greece (May 3, Tallaght Stadium), Czech Republic (May 6, RSC, Waterford), and Belgium (May 9, Tallaght Stadium).
Click here to secure tickets - only €5 for adults and FREE for Under-16s
Speaking on the Greatest League in the World podcast, Ireland Head Coach O'Brien believes home advantage will only come into play once people secure their tickets and turn up at the stadiums to support the boys in green.
"It's massive. I can't stress it enough to the public, this really is the biggest competition that they can play in. It's the best of the best in Europe coming to Ireland - there is going to be some serious quality on the doorstep and we have some quality in our team as well," said O'Brien.
"Even for our own development, to play in front of an Irish crowd, getting behind the team, we know how well our supporters get behind our teams, and we really need that. We will need that 12th man, because tournament football is demanding, you have three games in seven days.
"Every bit of support we can get, whether it is in Tallaght or coming down to the RSC, come out and support us."
O'Brien is finalising plans for what will be his third successive finals tournament at this level and he is excited by the opportunity afforded to his young players. Now, he wants the public to share in that enthusiasm.
This is a chance to see tomorrow's stars today and to get behind the Ireland team at a major tournament.
UEFA European Under-17 Championships - Fixtures
Friday, May 3: Republic of Ireland v Greece, Tallaght Stadium, KO 19:00
Monday, May 6: Republic of Ireland v Czech Republic, RSC, Waterford, KO 19:00
Thursday, May 9: Republic of Ireland v Belgium, Tallaght Stadium, KO 19:00
Click here to secure tickets - only €5 for adults and FREE for Under-16s