Summers, from Tifton, Georgia, will replace Willie Fritz, who left Georgia Southern to become Tulane's coach. Fritz was formally introduced as Tulane's coach Tuesday.
ESPN's Brett McMurphy and multiple outlets reported earlier that Summers had reached a verbal agreement to be Georgia Southern's new coach.
Summers served as an assistant coach at Georgia Southern in 2006 before stints at Alabama-Birmingham and Central Florida.
"I'm looking forward to building off the offense that is in place and continuing to progress with the defense,'' Summers said.
Georgia Southern plans to introduce Summers at a news conference on Saturday. Interim president Dr. Jean Bartels, athletic director Tom Kleinlein and the Georgia Southern board of regents announced Sunday night that Summers had accepted the offer from Georgia Southern.
Kleinlein said Summers is a "great fit'' for the Eagles.
"What we get in Tyson is someone who knows Georgia, someone who was born and raised in Georgia, someone who has recruited Georgia his entire career, and someone who has been a part of a ... school that has played on New Year's Day, which is the level we're aspiring to get to,'' Kleinlein said.
Georgia Southern will play Bowling Green in the GoDaddy Bowl in Mobile, Alabama, on Wednesday.
Summers' Colorado State defense ranks 20th in the nation in pass defense.
Information from The Associated Press contributed to this report.