Actor Lee Ingleby, who is starring in BBC One's Our Zoo, takes over from Neil Morrissey, who played the handyman from its launch in 1998.
Also joining the series when it airs next year will be Downton Abbey's Joanne Froggatt, who'll play Bob's business partner Wendy.
Inbetweeners star Blake Harrison voices the digger Scoop.
Ingleby, also known for his role as Stan Shunpike in Harry Potter And The Prisoner Of Azkaban, said: "I was very excited to be given the opportunity to be the voice of such a well-loved character.
"My little nephew is such a huge fan of Bob that I had to jump at the chance.
"Capturing a child's imagination is so important, and I just wish I was half as good at DIY as Bob is."
Froggatt said: "My godchildren are huge fans of the show so I'm looking forward to seeing their reactions when the new series begins.
"Wendy is a strong and positive female role model and I think it is important that children's television shows positive social values."
Viewers will see a big difference on screen as the characters will be computer-generated for the new series rather than created using stop-motion animation.
Bob also has a new home in the busy town of Spring City, and will use a computer for his building designs, but he'll still be seen working at his yard in the village of Fixham.
Harrison joked that the show was more family-friendly than his appearances in E4's Inbetweeners, which has also led to a pair of hit spin-off films.
"I'm really excited to be a part of such a long-running, successful series," he said.
"I'm even more excited to be involved in a project that my daughter can watch before she's 30.
"Working on an animation is completely new to me, but as a method actor I know only one way to prepare for a role, so I've painted myself yellow and am now offering to dig up anything you may need."
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After 16 years, Bob The Builder is having a makeover with a new look and voice.