"We've already had this conversation. We're in it for the long haul," Underwood explained, per TooFab. "I know you guys have opinions on prenups. We don't want to put those vibes out there."
As for when they'll tie the knot, Underwood noted that industry-wide delays due to the COVID-19 pandemic may necessitate waiting a bit.
"I want a good wedding," he said. "We need a venue and venues are backed up."
Underwood, who came out as gay in April 2021, also gushed over Brown while on the show.
"I went on a few dates. I only had to be gay five minutes to understand that there was nothing better than my connection with him," he said. "It was a pretty easy decision."
Underwood additionally opened up about how he feels now, nearly a year after coming out.
"All of the coverups, praying, trying self-conversion therapy on myself by being the Bachelor. I've pretty much tried anything to be straight and it didn't work," he said. "... I just love being gay now."
The reality star and the political strategist have been dating since the summer of 2021.
When ET spoke with the former Bachelor in support of his Netflix series, Coming Out Colton, he revealed why he wanted to keep his relationship with Brown relatively private.
"I've learned this new thing since I did The Bachelor -- it's called boundaries," Underwood quipped of his decision to stay mum about his relationship. "I finally put some up."
"Having a public relationship wasn't the healthiest thing last time," he told ET at the time. "I'm very happy. I'm in a very good place in my relationship with him. That's pretty much all I've got for you."
"After my birthday, Jordan and I went to Big Sur for a weekend getaway to decompress and relax in nature. I couldn't have pictured a more beautiful place to celebrate an amazing milestone in my life and relationship," he said. "I'm extremely happy! 2021 was the most transformative year of my life. Starting 2022 off with my best friend, teammate and now fiancé is something I never thought was going to be possible."