Speirs, 39, has been embroiled in controversy since he quit the leadership on August 8, declaring that he had "just had a gutful" of leadership speculation and did not have the energy to keep fighting.
On September 9, News Corp published a video purportedly showing Speirs snorting a powder.
He declared the footage to be a "deepfake" and vowed to clear his name.
Two days later, he took medical leave, saying the past few days had been "exceptionally distressing" and that he has been left "feeling exceptionally vulnerable and at risk".
On October 5, Speirs released a video statement saying he did not believe he could "adequately and effectively serve my local community while also dealing with this matter, protecting my mental health and supporting my family and friends".
"Since allegations of illicit substance use in my home became public, my home has been raided by armed police, I was arrested and I was questioned," he said.
Police confirmed Speirs was arrested at Berri, in SA's Riverland, on September 26 and charged with two counts of supplying a controlled substance from August 2-3 and on August 9.
He was granted bail and will face Christies Beach Magistrates Court, in Adelaide's southern suburbs, on Friday.
Speirs resigned from parliament on October 15, clearing the way for a by-election in his southern Adelaide seat this Saturday.
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