Barty, who continued her meteoric rise this season by capturing her maiden Grand Slam title at Roland Garros before taking over the No. 1 spot in rankings for the first time in her career in June, also took home record prize money of $4.42 million (about 3.95 million euros), Efe news reported.
"It has been a remarkable year (and) tonight was about coming out and fighting to the end. I couldn't be prouder," Barty said after the match.
Heading into Sunday's final, the 23-year-old Australian had a 0-5 career record against Svitolina, who rolled to a 7-6 (10-8), 5-7, 6-4 win over her earlier this year at Indian Wells.
"I'm proud of myself and the team, we tried to put ourselves in the biggest situations and occasions, and we managed to do that," Barty said.
The 25-year-old Svitolina, whose biggest career title came at last year's WTA Finals in Singapore, was seeking her first title of 2019 in Shenzhen.
Barty played aggressively from the start, breaking Svitolina four times and sealing the victory in one hour and 26 minutes.
The Australian, who also won the title in Miami this year, ensured that she finishes the year in the top spot of ATP rankings.
"You're one of the toughest competitors on the tour and I know we'll have many, many more battles in the future," Barty told Svitolina.
Barty is the first Australian to win the WTA Finals since 1976, when Evonne Goolagong Cawley won the title. Cawley had also won the title in 1974.
Last week, Barty said that she planned to give a big chunk of her prize money to the Royal Society for the Prevention of Cruelty to Animals (RSPCA) in Australia.
Barty, who is an ambassador for the animal welfare group, said that she had done a "little bit of online shopping because I know they're in need of kind of normal stuff for the cats and dogs and kind of everything at the RSPCA shelter."
"A little bit to give back to them when I'm back home in Australia at the end of the year. We're really excited to do it," Barty, who has four dogs, said.
In the doubles final, Hungary's Timea Babos and France's Kristina Mladenovic rolled to a 6-1, 6-3 win over Chinese Taipei's Hsieh Su-Wei and the Czech Republic's Barbora Strycova.
The duo, who needed just 65 minutes to book the win, became the first defending champions to retain the title at the event in 11 years.
The WTA Finals is the most prestigious event on the women's tennis calendar after the four Grand Slams.
( With inputs from IANS )