Timmons was drafted by the Pittsburgh Steelers 15th overall in the 2007 NFL Draft. He began his rookie season as the backup right outside linebacker to James Harrison. He made his professional debut in the Steelers' season opener against the Cleveland Browns, making one tackle in the Steelers' victory. The following week, he made a season-high two solo tackles during a 26–3 victory over the Buffalo Bills. As a rookie, he was used rarely as a rotational player and on special teams but appeared in all 16 regular-season contests. He made 13 tackles throughout his rookie season.