Ha Seung-jin attended his father's alma mater Samil Commercial High School in Suwon with his childhood friend Yang Hee-jong, who was a year older.

He initially planned on entering the 2003 NBA draft held in June but decided on playing college basketball first and accepted an early offer from Yonsei University.

[1] It meant that he would be allowed to join the Yonsei team for the 2003 fall semester despite still being a high school senior.

[2] His contemporaries at Yonsei included Yang and future Jeonju KCC Egis teammate Kim Tae-sul.

During the 2005-06 season Ha was assigned to the NBA D-League's Fort Worth Flyers on March 28, 2006,[6] where he played for five games but did not make an impact.

[8] Ha returned to South Korea and joined the 2008 Korean Basketball League draft, signing with Jeonju KCC Egis.

Their father Ha Dong-gi is a former basketball player-turned-coach who played for Myongji University and gave up the sport due to chronic injury problems.