[2] Yeo took part in the 2008 Pacific School Games in Canberra, Australia where she won five medals,[5][6][7] including gold in the 50-metre backstroke[8] and in the 4 × 50-metre freestyle relay.

[23][24][25] Another successful ASEAN School Games meet in Surabaya, Indonesia followed with Yeo picking six medals including two gold and another national under-17's record in the 4 × 100-metre freestyle relay.

[27][28] In the 200-metre breaststroke, Yeo won silver in a new national under-17's record time of 2:34.07,[29] shaving 0.22 seconds off Nicolette Teo's 11-year-old mark.

[31][32] In the heats of the 100-metre breaststroke, Yeo was the fastest qualifier in a meet record time of 1:12.58, eclipsing Cheryl Lim's 1:14.06 set in 2011.

[34] However, she later teamed up with Jing Wen Shan, Madeline Quek and Song Ai Vee to win gold in the 4 × 50-metre medley relay with 2:02.88, shaving 0.03 seconds off Raffles's 2012 meet record[35][36] and the same quartet won gold in the 4 × 50-metre freestyle relay in 1:50.44, narrowly missing the meet record of 1:49.24.

[39] Following a successful meet at the 33rd Southeast Asian Age Group Swimming Championships in Kuala Lumpur, Malaysia, where she picked up five medals,.

[41][42][43] She then lowered her personal best time in the 50-metre breaststroke to 33.35 at the 35th Southeast Asian Age Group Swimming Championships in Da Nang, Vietnam, where she won four medals.

[47][48] Yeo collected silver in the 100-metre breaststroke,[49] 200-metre breaststroke,[50] 4 × 100-metre medley relay with Marina Chan, Stacy Tan, Meagan Lim[51] and 4 × 100-metre freestyle relay alongside Chan, Hoong En Qi, Rachel Tseng in a new national under-17's record time of 3:54.67,[52] slashing 1.88 seconds from the previous mark.

[59] In November, at the final leg of the 2009 FINA Swimming World Cup in Singapore, Yeo reached the final of the three breaststroke events[60][61][62] then closed out the year by finishing fourth in the 200-metre breaststroke at the 2009 Southeast Asian Games in Vientiane, Laos in a new national under-14's record time of 2:36.04,[4][63] improving on Nicolette Teo's previous mark of 2:36.27 set at the 1999 Southeast Asian Games.

Stopping the clock at 1:14.05, this shaved 0.02 seconds off Joscelin Yeo's time set at the Asia Pacific Swimming Meet in September 1991.

[73] In June 2011, Yeo won her first national title in the 50-metre breaststroke at the Singapore Championships, finishing 0.20 seconds shy of Nicolette Teo's 2006 meet record of 33.49.

[74] In November, Yeo set a new national short course record of 32.90 in the 50-metre breaststroke at the Singaporean leg of the 2011 FINA Swimming World Cup[75][76] and finished the season with two medals at the 2011 Southeast Asian Games in Palembang, Indonesia.

This time also broke Joscelin Yeo's seven-year-old meet record of 1:12.36, and was achieved a mere 30 minutes after her silver medal in the 400-metre individual medley.

[89] In November, Yeo lowered her own national mark in the 50-metre breaststroke to 32.75 at the Tokyo leg of the 2012 FINA Swimming World Cup.

In the 4 × 100-metre medley relay, Yeo with Tao Li, Amanda Lim and Quah Ting Wen won gold in 4:13.02, extending Singapore's winning streak in the event to six.

[123] One month later at the 2014 Commonwealth Games in Glasgow, Yeo reached the semi-finals of the 50-metre breaststroke[124] before heading to the 2014 Summer Youth Olympics in Nanjing in August.

In September, Yeo competed at the 2014 Asian Games in Incheon, South Korea, where she just missed the final of the 50-metre breaststroke, finishing 9th in the semi-final in 33.26.