Mears started his rugby with Torquay Athletic minis and via Colston Collegiate School in Bristol he joined Bath Rugby Club where he has spent all his professional career.

He represented England 16 and 18 Groups, together with England Under 19 Colts and 21s, for whom he played in three World Championship matches in New Zealand. In 1997 he was a member of the unbeaten England U18 Schools party that toured Australia with fellow World Cup squad members Jonny Wilkinson, Andrew Sheridan and Steve Borthwick.

He also appeared for England A in two Churchill Cup tournaments (2004 and 2005) and captained Bath in the Middlesex Sevens (2006).

Before the 2007 Rugby World Cup, he played in 18 of England’s 22 tests dating back to his debut as a replacement for Steve Thompson against Samoa at Twickenham in 2005. More recently he has shrugged off the benchman tag to start England's last 13 games, most recently the 26-12 victory over Scotland.