Mr Wardell, 37, died in his sleep due to a “cardiac arrest” on Tuesday morning, Ms Archibald, 28, said.
Wardell had just won the elite men’s title at the Scottish MTB XC Championships at Kirroughtree Forest, and appeared on television on Monday night to celebrate.
The cyclist overcame two punctures to win the race, and joked on BBC Scotland’s The Nine programme that it had been “a bit of a disaster”.
Just hours later, he passed away, with Ms Archibald saying she “tried and tried” to save him.
The fellow cyclist said: “I still don’t understand what’s happened; if this is real; why he’d be taken now – so healthy and happy.
“He went into cardiac arrest while we were lying in bed. I tried and tried, and the paramedics arrived within minutes, but his heart stopped and they couldn’t bring him back.
“Mine stopped with it. I love him so much and need him here with me. I need him here so badly, but he’s gone. I can’t describe this pain.
“Thank you to those making tributes. I can’t bear to talk about him in the past tense to say anything myself.
“You mean everything to me, Rab. I love you.”
A statement from the Scottish Cross Country Association read: “Our deepest sympathy to his friends, family and loved ones.
“He will be truly missed by our community and his determination, talent and friendship will live on in all our hearts and memories.
“I’m sure more eloquent words will be written by many but RIP Rab. Our Champion, Our Inspiration, Our Friend.”
After he won gold in the Scottish championship Mr Wardell took to Twitter to celebrate the result. He said: “Scottish Champion. It’s taken a few years but I can now add the Senior Cross Country title to the Junior and U23 ones I won nearly 2 decades ago.”
His victory was described as a “show of incredible resilience” by British Cycling.
The six-time Olympic gold medallist Sir Chris Hoy tweeted: “Can’t believe this. Utterly heartbreaking. Rest in peace Rab.”
Mr Wardell lived with Ms Archibald in Glasgow.
He had been racing mountain bikes since he was a teenager.
The cycling champion had only turned professional earlier this year.
In a statement on Twitter, Scottish Cycling said: “We are devastated to confirm the news that international mountain biker & former employee, Rab Wardell, has passed away today.
“We have very little information at this stage, but we send our love & support to his family, friends & all those in our community who knew him.
“We ask that you respect Rab’s family’s privacy at this incredibly sad time.”