of one's own free will

/ɒv wˈɒnz ˈəʊn fɹˈiː wˈɪl/

/ʌv wˈʌnz ˈoʊn fɹˈiː wˈɪl/

de son plein gré

in a way that demonstrates one's capability and independence in decision-making free of any influence or circumstance