Katherine, who is several months pregnant, sported a black dress, tights and heels, cradling her bump as she arrived at the venue in Manchester.
The 33-year-old walked hand in hand with her husband Ryan Clark as the couple joined fellow partygoers Lisa Riley, Samia Ghadie and Suranne Jones as well as the birthday boy's other half, Corrie star Anthony Cotton.
Model and actress Catherine Tyldesley also attended the special event, wearing a V-necked blue dress adorned with sequins and a glittering floral headpiece.
Barnsley-born Katherine said that she and her Australian husband Ryan were "overjoyed" to find out that they were expecting their first baby.
"We've always said that having a family is not something we wanted to plan," Katherine told HELLO! shortly after announcing her pregnancy. "That it would happen when it was meant to happen. It just happened much quicker that we expected."
"It wasn't why we got married," added the Mr Selfridge star, in reference to her Las Vegas nuptials which took place less than a month earlier. "I would have been quite happy to have my child out of wedlock."
Katherine and digital analyst manager Ryan married in secret while on holiday in the US.
"The day was everything we hoped it would be - no fuss, low key, sunshine and just us!" said Katherine to HELLO! "We'd been laughing and joking all day and then suddenly, everything seemed to stop and we tried to get the words "I do" out without becoming emotional wrecks.
"It was awesome. I'll never forget that moment for the rest of my life."