According to the Idaho Legislature website, the bill was signed Thursday and will take effect July 1.
The law slaps drivers with an $85 fine for using smartphones and other hand-held devices to review, prepare, or send written communications.
(Hands-free devices are exempted.)
The bill's journey to the governor's desk has been a difficult one. For several years, it failed to clear the legislature and was dogged by what supporters considered frustrating set backs.
Some lawmakers felt the bill was simply unenforceable.
But legislators this session were under more pressure to act after recent traffic deaths linked to smartphone use.
Compelling testimony from the family of 18-year-old Taylor Sauer, who died in a highway crash while using her phone for social networking also played a role this year.
The original version of the law included and exemption for emergency responders and law enforcement.
However, after those agencies asked to not be exempt, the bill was amended to include them in the ban.
Now Idaho has joined 35 other states that ban text messaging for drivers.
The governor's office was unavailable for comment Thursday evening.