Timonen was drafted by the LA Kings in 1993 in the 10th round and 250th overall. After the draft, he continued to play in his native Finland for several years, first for KalPa and then later for TPS. In 1998, Timonen played on the bronze medal-winning Finnish Olympic team in Nagano. Shortly after the Olympics, he was traded, along with Jan Vopat, from the LA Kings to the Nashville Predators in agreement that Nashville would not select Garry Galley in the 1998 NHL Expansion Draft.
During the 1998–99 NHL season, Timonen split time between the Predators and their IHL affiliate, the Milwaukee Admirals. The following year, he was promoted to a full time NHL player. He played the next four seasons for the Predators, steadily improving his offensive output, until the 2004–05 NHL lockout. During the lockout, Timonen played for his hometown team, KalPa, which he partly owns with former Philadelphia Flyer teammate Sami Kapanen. Timonen also persuaded his fellow teammate Adam Hall to play for KalPa for the duration of the lockout.
Timonen represented Finland at the 2004 World Cup of Hockey and led his team in scoring with six points, the fifth-highest total overall in the tournament.
On October 3, 2006, Timonen was named the captain of the Nashville Predators for the 2006–07 season. That season proved to be a career year for Timonen with him registering career highs in both assists and total points.
Following the 2007 season, Timonen signed a six-year contract worth $37.8 million with the Philadelphia Flyers, which made him the highest paid Finn in the NHL. At the time, Timonen's younger brother Jussi Timonen was playing for the Philadelphia Phantoms, the AHL affiliate of the Flyers. However, Jussi was subsequently traded to the Dallas Stars.
Timonen's and the Flyers' great run in this season's playoffs was put on hold after a visit to the doctor; Timonen got hit by a wrist shot at his foot on April 30, 2008, by Montreal Canadiens defenseman Andrei Markov. Timonen felt numbness in his foot as the week went along and thought it was nothing but a twisted nerve. After an MRI failed to reveal anything, Timonen had the foot examined at the Hospital of the University of Pennsylvania. However on May 8, 2008, the doctor found a small blood clot in Timonen's foot. Timonen was sidelined indefinitely. After beating the Capitals 4-3, and the Canadiens 4-1, Timonen and the Flyers went on to play the Pittsburgh Penguins in the Eastern Conference Finals only to lose the series 4-1.
| Regular Season | Playoffs | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Season | Team | League | GP | G | A | Pts | PIM | GP | G | A | Pts | PIM | ||
| 1991–92 | KalPa | SM-l | 5 | 0 | 0 | 0 | 0 | -- | -- | -- | -- | -- | ||
| 1992–93 | KalPa | SM-l | 33 | 0 | 2 | 2 | 4 | -- | -- | -- | -- | -- | ||
| 1993–94 | KalPa | SM-l | 46 | 6 | 7 | 13 | 55 | -- | -- | -- | -- | -- | ||
| 1994–95 | TPS | SM-l | 45 | 3 | 4 | 7 | 10 | 13 | 0 | 1 | 1 | 11 | ||
| 1995–96 | TPS | SM-l | 48 | 3 | 21 | 24 | 22 | 9 | 1 | 2 | 3 | 12 | ||
| 1996–97 | TPS | SM-l | 50 | 10 | 14 | 24 | 18 | 12 | 2 | 7 | 9 | 8 | ||
| 1997–98 | HIFK | SM-l | 45 | 10 | 15 | 25 | 24 | 9 | 3 | 4 | 7 | 8 | ||
| 1998–99 | Nashville Predators | NHL | 50 | 4 | 8 | 12 | 30 | -- | -- | -- | -- | -- | ||
| 1998–99 | Milwaukee Admirals | IHL | 29 | 2 | 13 | 15 | 22 | -- | -- | -- | -- | -- | ||
| 1999–2000 | Nashville Predators | NHL | 51 | 8 | 25 | 33 | 26 | -- | -- | -- | -- | -- | ||
| 2000–01 | Nashville Predators | NHL | 82 | 12 | 13 | 25 | 50 | -- | -- | -- | -- | -- | ||
| 2001–02 | Nashville Predators | NHL | 82 | 13 | 29 | 42 | 28 | -- | -- | -- | -- | -- | ||
| 2002–03 | Nashville Predators | NHL | 72 | 6 | 34 | 40 | 46 | -- | -- | -- | -- | -- | ||
| 2003–04 | Nashville Predators | NHL | 77 | 12 | 32 | 44 | 52 | 6 | 0 | 0 | 0 | 10 | ||
| 2004–05 | HC Lugano | Swiss-A | 3 | 0 | 1 | 1 | 0 | -- | -- | -- | -- | -- | ||
| 2004–05 | Brynäs IF | SEL | 10 | 5 | 3 | 8 | 8 | -- | -- | -- | -- | -- | ||
| 2005–06 | Nashville Predators | NHL | 79 | 11 | 39 | 50 | 74 | 5 | 1 | 3 | 4 | 4 | ||
| 2006–07 | Nashville Predators | NHL | 80 | 13 | 42 | 55 | 42 | 5 | 0 | 2 | 2 | 4 | ||
| 2007–08 | Philadelphia Flyers | NHL | 77 | 8 | 36 | 44 | 48 | 13 | 0 | 6 | 6 | 8 | ||
| NHL Totals | 611 | 84 | 236 | 320 | 372 | 29 | 1 | 11 | 12 | 26 | ||||
International statistics
| Year | Team | Event | GP | G | A | Pts | PIM |
|---|---|---|---|---|---|---|---|
| 2001 | Finland | WC | 9 | 2 | 2 | 4 | 10 |
| 2002 | Finland | WC | 9 | 1 | 2 | 3 | 8 |
| 2003 | Finland | WC | 7 | 2 | 5 | 7 | 2 |
| 2004 | Finland | WCH | 6 | 1 | 5 | 6 | 2 |
| 2005 | Finland | WC | 6 | 2 | 1 | 3 | 6 |