Mike Johnson, the newly elected Republican speaker of the US House, won taxpayer funding for a Noah’s Ark amusement park while working as a lawyer, in a graphic illustration of his uncompromising rightwing Christian beliefs.

Working for Freedom Guard, a non-profit proclaiming a commitment to defending religious liberty, Johnson was hired by Answers in Genesis, a creationist ministry, in 2015, after the state of Kentucky rescinded an offer of tourism tax incentives for the project in Williamstown, citing discrimination against non-Christians.

The state retracted an offer of tax breaks after the then-governor, Steve Beshear, said the ministry reneged on a commitment to refrain from hiring based on religious belief.

“It has become clear that they do intend to use religious beliefs as a litmus test for hiring decisions,” Beshear said.

Johnson, who would win a seat in Congress from Louisiana in 2016, was among a team of attorneys engaged to press a federal lawsuit described by the Answers in Genesis president and chief executive, Ken Ham, as involving “freedom of religion, free exercise of religion, freedom of speech in this great nation of America”.

Johnson accused the state of “viewpoint discrimination”, adding: “They have decided to exclude this organisation from a tax rebate programme that’s offered to all applications across the state.”

Writing in the Louisville Courier-Journal, Johnson attributed opposition to the project to “a few radical secularists and others” who he said were misrepresenting the US constitution.

“One would expect that any project that will bring millions of dollars in new capital investment, create hundreds of jobs and be a tremendous asset to the communities of northern Kentucky would be enthusiastically welcomed by every Kentuckian,” he wrote.

“Just as every rational person understands the commonwealth was not somehow ‘endorsing’ the consumption of alcohol when it approved tax refunds for a beer distillery tour project in 2012, or ‘endorsing’ the speech of every stand-up comedian or adult-themed entertainer who may fill the stage at one of the entertainment venues previously approved, there can be no valid argument that the commonwealth will somehow endorse the private religious speech or viewpoints that may be expressed at the Ark Encounter Park.”

In the event, the case was won and the park – featuring a vast Ark-like structure meant to depict that in the biblical flood narrative as described in the Book of Genesis – went ahead. By 2017, it had received $18m in tax incentives, according to the Huffington Post.

The episode has been highlighted as emblematic of Johnson’s religious convictions, as Democrats seek to shed light on a previously little-known political figure who emerged as speaker only after three more prominent Republicans failed to gather sufficient support.

Johnson, 51, gained the backing of the Republican House conference following the intervention of Donald Trump, who publicly endorsed a man who actively supported his attempt to overturn the 2020 presidential election and was a member of his defence team during his first impeachment.

Johnson’s detractors say his religious beliefs have shaped his positions on a range of social issues, including divorce, LGBTQ+ rights and abortion, on which he has actively supported restrictive stances.

He expressed his views on secularism in a speech on the House floor this year, discussing “so-called separation of church and state” and arguing that the constitution did not prohibit the government from supporting religious beliefs.