World number five Kvitova, 25, beat five-time Grand Slam winner Maria Sharapova 6-3 7-6 (7-3) in Saturday's second semi-final.
Earlier, Radwanska, 26, overcame Spain's world number three Garbine Muguruza 6-7 (5-7) 6-3 7-5.
It will be Radwanska's first final at the event in her seventh appearance.
The world number six made the decisive break in the 12th game of the third set to finally break the Spaniard's resistance.
"It was a great match from the beginning to the end, lots of ups and downs, so many rallies and a lot of running," Radwanska said.
Radwanska had taken a 3-0 lead in the first-set tie-break before eventually losing it 7-5.
"I didn't know I could come back after that first set -  I am just so glad I could win that match," she said.
In the second semi-final, Kvitova broke in the seventh and ninth games to take the first set against Sharapova, who had won all three of her round-robin ties despite arriving in Singapore after a long injury lay-off.
The world number four hit back to take a 5-1 lead in the second set, but 2011 champion Kvitova rediscovered her rhythm to claim the victory in straight sets.

A team of three male candidates was selected last month which resulted in Michelle Gildernew being left off the ticket.
The meeting gives the former MP and minister another opportunity to be put on Sinn Féin's list.
Ms Gildernew had been replaced on the ticket by current MLA Phil Flanagan.
Analysis: 'Major embarrassment' for Sinn Féin
He had missed out on selection at a previous convention almost two months ago.
In December, Ms Gildernew was selected to run alongside sitting MLA Sean Lynch and local councillor John Feely.
However, Sinn Fein's ruling council (Ard Comhairle) ordered a revote.
The party did not specify why, but it has been reported that concerns had been raised about procedural errors.
A new convention at the end of January in Enniskillen replaced Ms Gildernew with Mr Flanagan, who will now stand alongside Mr Lynch and Mr Feely.
In December, the outgoing MLA Bronwyn McGahan announced she would not be seeking re-election.
However, Ms McGahan did put her name forward for the latest convention but was not successful.

Sajjad Ahmad, 37, was the driver of a Mercedes which was involved in a collision with a van between Polmont and Linlithgow on Friday evening.
His death on Tuesday followed his wife, Saadia, 37, who died at the scene and their nine-year-old daughter, Ayesha, who died in hospital on Saturday.
Mark Hansen, 42, the driver of a white Vauxhall van, died at the scene.
The Ahmads' two sons remain in hospital.
The motorway was closed between Junctions 3 and 4 southbound until 04:00 on Saturday for a police investigation.
Sgt Scott Sneddon, of Police Scotland, said: "Our sincere condolences go to the Ahmad family, who have asked that their privacy be respected at this tragic time.
"Our inquiries continue to establish the full circumstances surrounding this collision, and I'd like to thank the witnesses who have so far come forward.
"Anyone who witnessed the collision, saw either of the vehicles shortly beforehand, or has any information about this and has not yet been in contact is urged to get in touch."
Petra Kvitova of the Czech Republic will meet Poland's Agnieszka Radwanska in the final of the WTA Finals in Singapore on Sunday.
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Sinn Féin is to meet next week to select a fourth candidate in Fermanagh and South Tyrone for this year's assembly election.
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A fourth person has died following a serious crash on the M9 in West Lothian last week.