The phrase "to become legal" means to be made lawful or acceptable according to the rules and regulations of a particular place or system. Full definition
Marriage between same - sex couples became legal in 2013. (newlawjournal.co.uk)
Once every year, virtually all crimes become legal for 12 hours during which people are free to do whatever they want without fear of consequences. (gizmodo.com)
He was a technology lawyer before becoming a legal tech expert. (evolvelawnow.com)