Kromowidjojo won a total of three medals at the European Junior Swimming Championships in 2005 and 2006, in the 50 meter freestyle and butterfly events.

She won her first international senior medal in the 4 × 100 m freestyle relay, alongside Inge Dekker, Chantal Groot and Marleen Veldhuis, at the age of 15.

At the World LC Championships 2007 in Melbourne, Australia, she won a bronze medal in the 4×100 freestyle relay together with Inge Dekker, Femke Heemskerk and Marleen Veldhuis.

There she swam another world record in the 4 × 50 m freestyle short course with Hinkelien Schreuder, Inge Dekker and Marleen Veldhuis.

In the 4 × 100 m freestyle, she won the gold medal and with the team: Inge Dekker, Femke Heemskerk and Marleen Veldhuis.

She also won a gold medal as part of the 4 × 100 m freestyle relay team alongside Inge Dekker, Femke Heemskerk and Hinkelien Schreuder with another championship record of 3:28.54.

Individually she won a bronze medal in the 100m freestyle with a time of 53.66 behind Jeanette Ottesen and Aleksandra Gerasimenya who tied for first in 53.45.

At the 2012 Summer Olympics in London, Kromowidjojo and her teammates started the meet with a silver medal in the 4 × 100 m freestyle relay, an event in which they were the defending champions.

The next day in the final she followed this up by winning a gold medal in a new Olympic record of 53.00 seconds, ahead of reigning world champion Aleksandra Gerasimenya and Tang Yi.

In the final she completed the sprint double by winning a gold medal in a new Olympic record of 24.05 seconds, again beating Gerasimenya, as well as training partner and compatriot Marleen Veldhuis.

By winning the 50 m and 100 m freestyle, Kromowidjojo followed in the footsteps of compatriot Inge de Bruijn, who won both events at the 2000 Olympics in Sydney.

She lost her world title in the 50 meter freestyle to Bronte Campbell of Australia, winning the silver medal 0.10 s behind.

She represented the Netherlands at the 2019 World Aquatics Championships and won the silver medal in the women's 50 metre butterfly event.

She suffered viral meningitis while training with her national team in the Canary Islands in July 2010, but recovered to take part in the World Championships later that year.