The move comes as social media platforms face the threat of U.S. regulation over the lack of disclosure on such spending.
The database called "Ad Archive Report" will be updated weekly with details on who spent how much for political ads.
For example, The Trump Make America Great Again Committee, a fundraising organization for President Donald Trump, was second during the period with spending of $3.1 million.
O'Rourke, whose Beto for Texas campaign shelled out $5.37 million on Facebook sites from May to Oct. 20, was the biggest spender in that period on ads "related to politics and issues of national importance," Facebook said.
The report, which houses political ads for up to seven years, will be available to anyone regardless of whether they are a Facebook user or not, the company said.
Google launched a similar feature in August.