Singer songwriter Stefani, 51, and country music star Shelton, 45, announced their engagement in October last year.
The duo have been together for more than five years after meeting when they were coaches on the US version of TV talent show The Voice.
In fact there have been whispers Stefani and Shelton could get married as soon as this weekend, TMZ reported.
They could be heading down the aisle in just a few days time as the pair applied for a marriage licence earlier this week.
In the state of Oklahoma, the marriage licence is only valid for 10 days.
The award-winning musicians have released several songs together, including Nobody But You, which reached number 18 on the Billboard Hot 100 last year.
Stefani was previously married to Gavin Rossdale but the couple divorced in 2016.
The exes sharethree sons Zumo, Apollo and Kingston.
While Shelton divorced singer Miranda Lambert in July 2015 after four years of marriage.
Earlier this year, the Hollaback Girl hitmaker gushed over the “romantic” way they decided they were going to get married.
“I think in a romantic way, when you fall in love so hard and so unexpectedly — and so late in your life — you think ‘I want to marry you!’ That’s the first romantic reaction, like, ‘Let’s get married,’” she told Hoda Kotb on the Today show.
“He’s so gifted and so unique and talented and he really is my best friend. I feel just so excited that I have someone in my life that now I have a chance at happiness for a long time to come and it’s just a blessing, the whole thing, and it is a miracle.”