Lankford attended Lakeview Centennial High School in Garland. While there, he participated in the Close Up Washington civic education program. He earned a Bachelor of Science degree in Secondary Education (specializing in speech and history) at University of Texas at Austin in 1990, and a master’s degree in Divinity at Southwestern Baptist Theological Seminary in 1994. He was a substitute teacher and speech team assistant teacher at Pflugerville High School in 1991.

Lankford supported Oklahoma Question 711, a statewide constitutional ban on same-sex marriage and civil unions that passed in 2004 with 75% of the vote and remained law until it was challenged in court and struck down by a federal judge as unconstitutional in 2014. Lankford lambasted the decision, saying that “marriage is a state issue and Oklahoma has spoken.” He also endorsed the Defense of Marriage Act and condemned the 2013 Supreme Court decision striking down parts of the law.

In 2012, five days after President Barack Obama announced his support for same-sex marriage, the first sitting U.S. president to do so, Lankford told a ThinkProgress interviewer that he believed homosexuality is a choice and that employers should be allowed to terminate workers for their sexual orientation: “I think it’s a choice issue.” After LGBT advocates condemned his statements, Lankford defended himself on local television, reiterating his view that homosexuality is a choice.

Lankford has defended businesses and individuals opposing LGBT rights, including Chick-fil-A in the wake of its denunciation over donations to groups opposing same-sex marriage, and Phil Robertson after he was suspended from Duck Dynasty in 2013 following comments regarded as anti-LGBT and racist. Lankford attacked A&E for suspending Robertson, writing that Robertson “should be able to speak his views without fear of being silenced.”

In January 2014, Lankford announced he would run in the 2014 Senate special election to succeed retiring Republican Senator Tom Coburn. Lankford won the June 2014 Republican primary, defeating former state House speaker T.W. Shannon and former state senator Randy Brogdon. In November, Lankford won the election for the final two years of Coburn’s second term, defeating retiring state senator Constance N. Johnson by a margin of 557,002, 67.9%, to Johnson’s 237,923, 29.0%, with independent candidate Mark Beard collecting 25,965 votes, 3.2% of the total.

Lankford was elected to a full six-year term in the Senate at the 2016 Oklahoma United States Senate election, defeating Democratic consultant Mike Workman with 67.7 percent of the vote. As in 2014, he won in a landslide, carrying every county in the state.

In 2014 Lankford was endorsed by the National Rifle Association and had an “A” rating for his consistent support of pro-gun legislation. Lankford supports loosening restrictions on interstate gun purchases. He opposes firearm microstamping, a controversial method of imprinting casings with a unique marking to match it with a specific firearm, and would allow veterans to register unlicensed firearms.

Lankford was sworn into office on January 6, 2015, by Vice President Joe Biden.

The Human Rights Campaign, the largest organization advocating for LGBT rights in the United States, included Lankford in its 2016 “Congressional Hall of Shame” along with Senators Mike Lee and Ted Cruz.

On December 21, 2017, Lankford was one of six senators to introduce the Secure Elections Act, legislation authorizing block grants to states to update outdated voting technology as well as form a program for an independent panel of experts that would work toward the development of cybersecurity guidelines for election systems that states could then implement, along with offering states resources to install the recommendations.

After the 2018 Stoneman Douglas High School shooting in which the perpetrator used a Smith & Wesson M&P15 AR-15 style rifle to kill 17 and wound 17 others, Lankford said on NBC News’ Meet the Press he was open to requiring more comprehensive background checks for firearm purchases, saying, “The problem is not owning an AR-15, it’s the person who owns it.”

In August 2018, Lankford, Marco Rubio and 15 other lawmakers urged the Trump administration to impose sanctions under the Global Magnitsky Act against Chinese officials responsible for human rights abuses in western China’s Xinjiang region. They wrote: “The detention of as many as a million or more Uyghurs and other predominantly Muslim ethnic minorities in “political reeducation” centers or camps requires a tough, targeted, and global response.”

In June 2020 Lankford criticized President Trump’s decision to walk to the St John’s Episcopal Church near the White House, calling it “confrontational”. In a BBC interview he said that racism passes on from one generation to the next, and he challenged families to invite a family of a different ethnicity to their home for a meal, to “allow friendship to develop where there has only been friendliness in the past”.