With her improved ranking, Kenin was able to play primarily on the WTA Tour in 2018. She began the year by reaching her first WTA quarterfinal at the Auckland Open. After losing her first-round match at the Australian Open, Kenin produced good results at both Premier Mandatory events in March. She entered the top 100 by reaching the second round of the Indian Wells Open as a qualifier. She then qualified for and reached the third round of the Miami Open, where she upset No. 11 Daria Kasatkina.
Facebook customer Global Science Research sold information on over 87 million Facebook users to Cambridge Analytica, a political data analysis firm. According to The Guardian both Facebook and Cambridge Analytica threatened to sue the newspaper if it published the story. After publication, Facebook claimed that it had been "lied to". On March 23, 2018, The English High Court granted an application by the Information Commissioner's Office for a warrant to search Cambridge Analytica's London offices, ending a standoff between Facebook and the Information Commissioner over responsibility.
On 20 April 2018, Ardern attended the Commonwealth Heads of Government Meeting 2018 in London, where she was selected to deliver a toast to the Commonwealth at a state banquet of world leaders. She also had her first private audience with Queen Elizabeth II.
In preparation for the wedding, the Archbishop of Canterbury, Justin Welby, baptized Markle and confirmed her into the Church of England on March 6, 2018. The private ceremony, performed with water from the River Jordan, took place in the Chapel Royal at St James's Palace. The marriage ceremony was held on May 19 at St George's Chapel, Windsor Castle.
In July 2018, the UK government published the Chequers plan, its aims for the future relationship to be determined in the negotiations. The plan sought to keep UK access to the single market for goods, but not necessarily for services, while allowing for an independent trade policy. The plan caused cabinet resignations, including Brexit Secretary David Davis and Foreign Secretary Boris Johnson.
On 13 November 2018, UK and EU negotiators agreed the text of a draft withdrawal agreement, and May secured her cabinet's backing of the deal the following day, though Brexit Secretary Dominic Raab resigned over "fatal flaws" in the agreement. On 25 November, all 27 leaders of the remaining EU countries endorsed the agreement.
On 10 December 2018, the Prime Minister postponed the vote in the House of Commons on her Brexit deal. The announcement came minutes after the Prime Minister's Office confirmed the vote would be going ahead.