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.

Rio's offer of 16.50 Australian dollars ($16.42; Â£10.14) is now conditional on 47% of shareholders accepting it by 6 April.
Previously its minimum target was 50%.
The move came after talks on the A$3.9bn offer between Rio and Riversdale major shareholder, Brazil's CSN.
If it fails to reach the new threshold, Rio Tinto will pay Riversdale shareholders only A$16 a share.
So far only 41% have said yes.
The other key shareholder in Riversdale is Tata Steel of India, which recently increased its stake to 27% and also has a director on the company's board.
CSN, Brazil's largest steelmaker, has also increased its Riversdale stake to 19.9%.

The toilet, in a busy park in Pudong New Area, will have 10 unisex stalls, plus some urinals and a stall for disabled people.
The opening on 19 November will coincide with World Toilet Day.
Unisex facilities will spare officials having to decide how to share out male and female stalls, say reports.
"It is an apparent problem that women have to wait in lines for toilets," Fu Liping, an official involved in the project, was quoted as saying, by the Xinhua news agency.
The stalls will be more spacious than regular ones. To guarantee safety and privacy, there will be attendants and higher partitions between stalls.
But there are no plans yet to build more unisex toilets, as authorities are unsure whether citizens will embrace the idea.
Their caution seem to be well-grounded, as people online have been less than enthusiastic about the unisex lavatory.
"I don't really support the idea. After all, men and female are different," said Weibo user Zhu Zhu Xia.
Another Weibo user said: "The problem will be solved if they build double female toilets."
BBC newsreader Sophie Raworth is to be part of Watchdog's new presenting team.
[NEXT_CONCEPT]
Mining giant Rio Tinto has lowered its minimum acceptances target slightly in a last ditch effort to takeover South Africa's Riversdale Mining.
[NEXT_CONCEPT]
Shanghai is trialling a unisex public toilet block to lower the time women have to spend waiting in queues, Chinese media have reported.