On Sunday's episode of the Showtime series, Spencer received anti-terror training from Cohen, who was posing as a former member of the Mossad.
Spencer apologized on Monday, but said he won't resign for "this ridiculously ugly episode". He has served four terms and is still in office, but was defeated by political newcomer Steven Sainz in the Republican primary in May.
Georgia Gov. Nathan Deal (R) echoed those comments, saying he was "disgusted" by Spencer's actions.
Ralston and others had called for Spencer's immediate resignation.
According to CNN, he has also written to David Ralston, the House Speaker of the Georgia House of Representatives, to let him know that he was resigning from office, effective July 31.
The move came after Cohen told him it would incite fear in homophobic jihadists. He said he was told that the tactics would deter "what I believed was an inevitable attack".More news: Cort Nielsen takes win, Thomas in yellow ahead…
He added, "I deeply regret the language I used at his request as well as my participation in the "class" in general".
Spencer also repeatedly yelled the n-word after he was told to demonstrate how to attract attention while facing an ISIS kidnapper. "If I had not been so distracted by my fears, I never would have agreed to participate in the first place". "It is the n-word", he says.
Image: Capt Erran Morad is one of Baron Cohen's new creations.
In a statement, Spencer said he had received countless death threats after he introduced legislation in 2016 in an attempt to ban burqas.
In Sunday's episode, Spencer - who thought he was participating in an anti-terrorism training - pulled down his trousers and repeatedly chased Cohen's character yelling "USA motherf-ker" as a means "to intimidate ISIS", according to Cohen's character.
After the video aired this past weekend, Spencer was forced to resign.