The Doctor Strange star revealed his pride at all his friend has achieved during an appearance on ITV's This Morning on Wednesday.
"I'm so proud of him," Benedict said. "He's a friend and I've seen a bit of Judge Rinder and I know Rob Rinder and to see someone I know doing that is phenomenal."
Benedict Cumberbatch said it is "phenomenal" to see Judge Rinder on Strictly
Benedict and Rob first met when they were both students at Manchester University, and have been good friends ever since. The pair are so close that Judge Rinder star Rob even asked Benedict to officiate his wedding to partner Seth Cummings in Ibiza in 2013.
Speaking about his pivotal role in the ceremony at the time, Rob told The Sun it was a "very private, lovely thing to be asked to do."
But despite seeing his friend impress on the BBC show alongside his professional dance partner Oksana Platero, Benedict has ruled out competing on Strictly Come Dancing for now.
Benedict officiated at Rob's wedding
"I'm nowhere near their standard [at dancing] so I think I'll give that a miss for now," he said.
The 40-year-old has plenty of other things to keep him occupied included focusing on his family following the news that he and his wife Sophie Hunter are expecting their second child together, just 16 months after the birth of their son Christopher.
"I'm still trying to find myself as a dad," Benedict admitted, adding: "We are expecting our second. I'm very excited. I'll be there all the way, absolutely."
The couple told E! last week that they were "absolutely thrilled" to be expecting another baby, with Sophie proudly showing off her growing bump at a screening of Doctor Strange at Westminster Abbey, London on Monday night.