When he and Heinonen started at Suutarila high school in the early 1990s, they met Pauli Rantasalmi and later Janne Heiskanen.

In 1998, after having released three albums, Janne Heiskanen left and in 1999 Aki Hakala became The Rasmus' new drummer.

In the same year, the band's former manager Teja Kotilainen left their current record label, Warner Music Finland.

Lauri sang co-vocals with Siiri Nordin, the singer of Killer, on a b-side version of the group's single, "All I Want".

In 2004, Ylönen recorded a song together with Apocalyptica and HIM's singer Ville Valo, named "Bittersweet".

is taken from the same album as "Bittersweet" Ylönen also sang, with other members Kwan and Siiri Nordin of Killer, a song called "Chillin' at the Grotto" at a gala.

Most recently, Ylönen announced a solo album scheduled for release in March 2011 with the first single Heavy being out in February.

Ylönen stated that he wanted several songs, that did not fit The Rasmus, to be released as a major record rather than a demo or something like that.

Ylönen announced via his official website that he would continue his European tour starting with two dates in Russia for 2012.

[4] He has a son named Julius, born in April 2008, with Finnish singer Paula Vesala[5][6][7] whom he married on 8 November 2014 in Las Vegas.