Second seed Garbine Muguruza is the leading player in the white group which comprises third seed Karolina Pliskova, fifth seed Venus Williams and the French Open champion Jelena Ostapenko. The 20-year-old from Latvia is also making her first appearance at the event.
A round robin will decide the top two from each group and they will advance to the semi-finals. The final will take place on 29 October at the Singapore Indoor Stadium.
Of the eight players, only 37-year-old Williams has won the title before. Her triumph came in Doha in 2008 when she came from a set down to dispose of the Russian Vera Zvonareva.
Since rankings were computerised in 1975, 25 women have held the number one spot but only 12 have finished the season in top place.
With up to 1,500 points available at the event, seven women have the opportunity to finish the season with the kudos of being world number one on 31 December.
Halep took pole position on 9 October after the China Open where she lost in the final to Garcia, who is the first French player to appear at the elite event since Marion Bartoli in 2007.
"I'm proud that I could qualify for the fourth time in a row," said Halep. "It's a great thing as it shows that I am very consistent. I'm in the top for the last four years. It's a great feeling."
The 26-year-old Romanian holds a 40 point lead over Muguruza, who saw off Williams to win Wimbledon in July. Ostapenko, who sits 1,165 points behind Halep, is also within sight of ending the year as queen of the circuit after starting it in 44th place.