The cultured centre-back has moved to the Banks's Stadium on a deal until the end of the season and adds some much needed competition to the Saddlers' defence.
Bielik enjoyed a successful loan spell at Birmingham last season with the 20-year-old impressing in 10 appearances for the club.
The Poland under-19 international has spent the last three months on the sidelines after he underwent surgery on his shoulder.
And Arsenal have now granted him a loan move to Walsall so he can regain his match fitness by playing first-team football.
Bielik has joined the Saddlers despite interest from a host of clubs in League One and abroad.
And boss Jon Whitney admitted he was delighted to land the defender having chased him for a number of weeks.
“Krystian is a very technical, ball-playing centre-half and he’s had a good loan spell with Birmingham last season, so he’s got a Midlands connection,” Whitney said.
“He was really good for them but he’s had a shoulder injury in the last few months.
“I’ve been chasing him for about two or three weeks now, and we’ve persuaded him to come here ahead of other League One clubs and some abroad, too.
“We’d like to thank Arsenal and Arsene Wenger for allowing him to come to us.”