Raworth and Michelle Ackerley, formerly a reporter on the BBC One consumer show, will join Matt Allwright and Chris Hollins when its new series begins next month.
Anne Robinson's departure from Watchdog after 12 years on the programme was announced earlier this month.
Raworth's addition to the line-up comes more than 30 years after her completing work experience on the show.
"Watchdog is the reason I got into television," she said. "After doing two weeks work experience on the programme when I was 16, I was determined to become a journalist.
"I've presented Watchdog Daily and Test House for the past three years. I'm delighted to have been asked to join Matt, Chris and Michelle for the new series. It feels like I've come full circle."
Ackerley joined the BBC in 2005 and has previously reported for Watchdog and the Crimewatch Roadshow.
"I'm passionate about uncovering and investigating new stories and excited to work with Matt, Chris and Sophie," she said.
"I'm genuinely excited to be part of such a fantastic team."
The new series of Watchdog starts on 8 October.
BBC newsreader Sophie Raworth is to be part of Watchdog's new presenting team.