A cause celebre is something that garners a lot of public attention, usually a famous incident or legal case. It literally means famous case in French.
Also, In French it is spelled , but the accent marks are usually omitted in English, as shown by the ngram below. It is grammatically correct either way.
The plural is causes celebres or causes célèbres.
Examples
The cases of Rojo and Slimani became Sporting’s cause célèbre of the summer, the hierarchy outraged at perceived “breaches of contractual duties” given their clear desire to leave. [The Guardian]
It is a cause célèbre for campaigners determined to save the French from turning into a nation of Coke-guzzling hamburger munchers. [The Telegraph]
The strike at Greyhound Recycling is now the most bitter and divisive trade dispute in recent years. It has also become a cause celebre among not just the trade union movement but leftist groupings such as Dublin Says No as well as supporters of People Before Profit who have sometimes joined the SIPTU and other workers on the picket. [Irish Independent]
By the late sixties and seventies, causes celebres like Vietnam and Bangladesh were precipitating ideas as the basis of economic and political theory and policy. [Mainstream]
Decades later, in exile on St Helena, Napoleon declared that “the queen’s death must be dated from the diamond necklace trial”. Amid the thicket of lies, self-delusion and misunderstandings that characterise one of the great causes célèbres of the 18th century, all the trails lead back to that night in the gardens of Versailles. [The Telegraph]