The legislation, which is one of several anti-abortion measures advanced by the state's Republican-controlled legislature this year, will take effect this summer unless it is blocked in court.
"We want to choose life in Oklahoma. We do not want to allow abortions in the state of Oklahoma," Stitt said as he signed the bill at a news conference on Tuesday.
If it takes effect, the ban will widen a swath of the country where there is little to no legal abortion access.
Oklahoma has become a frequent destination for Texas women seeking abortions since the larger neighboring state in September banned abortions for pregnancies from about six weeks, before many women even know they are pregnant.
Planned Parenthood abortion providers in Oklahoma saw a nearly 2500 per cent increase in Texas patients in the months after the Texas law took effect compared to the same period in 2020, the organisation said.
"The ban signed today is cruel and if it takes effect this summer, will have a devastating impact on people in Oklahoma, neighboring Texans, as well as an entire region facing attacks on their rights to abortion access," Melissa Fowler, the National Abortion Federation's chief program officer, said in a statement.
Separate legislation introduced in Oklahoma this year proposes banning almost all abortions and relying on private citizens to sue any person who "aids or abets" abortions, similar to Texas' six-week abortion ban.
That bill contains an emergency clause, which would allow it to take effect immediately once it is signed by the governor.
In the past few months, Republican-led states like Oklahoma have been quickly passing ever-stricter abortion bans with the anticipation that an impending US Supreme Court decision could help the bans withstand legal challenges.
The Supreme Court is due to rule by the end of June on a case involving a Republican-backed Mississippi law that gives its conservative majority a chance to undermine or even repeal the landmark 1973 Roe v Wade ruling that legalised abortion nationwide.
During arguments in the case, the conservative justices signaled a willingness to dramatically curtail abortion rights in the United States.
