Onassis is a competitive show jumper in select events of the Global Champions Tour.
She began riding as a child, and finished second in an event in Jerez, Spain in 2001.
She later chose to compete as a Greek citizen for the Avlona Riding Club in Athens, under the name "Athina Onassis".
In November 2012, Onassis suffered a spinal injury in a fall from her horse, but represented Greece in the 2013 European Show Jumping Championships and the 2014 World Championships.

Onassis is also a patroness of the Global Champions Tour.
The Athina Onassis International Horse Show, a show jumping competition, was established in 2007 in São Paulo and moved to Rio de Janeiro in 2009.
In 2014, the competition moved to Pampelonne beach in Saint-Tropez, France.
Onassis and her former husband were joint owners of AD Sport Horses, a horse breeding and training business based in Fleurus, Belgium.
In February 2014, Onassis paid $12 million for a 2.3-hectare (5.6-acre) estate and barn in Wellington, Florida.
She sold the estate in April 2017 for $12.75 million.
Onassis is a competitive show jumper in select events of the Global Champions Tour. She began riding as a child, and finished second in an event in Jerez, Spain in 2001. She later chose to compete as a Greek citizen for the Avlona Riding Club in Athens, under the name "Athina Onassis". In November 2012, Onassis suffered a spinal injury in a fall from her horse, but represented Greece in the 2013 European Show Jumping Championships and the 2014 World Championships.
Onassis is also a patroness of the Global Champions Tour. The Athina Onassis International Horse Show, a show jumping competition, was established in 2007 in São Paulo and moved to Rio de Janeiro in 2009. In 2014, the competition moved to Pampelonne beach in Saint-Tropez, France. Onassis and her former husband were joint owners of AD Sport Horses, a horse breeding and training business based in Fleurus, Belgium. In February 2014, Onassis paid $12 million for a 2.3-hectare (5.6-acre) estate and barn in Wellington, Florida. She sold the estate in April 2017 for $12.75 million.
Athina Onassis