take matters into one’s own hands

自分でなんとかする、自ら行動を起こす。(本来解決すべき人が達成・対処できなかったことを)

Ex

  • He was able to take matters into his own hands.

Reference source

  • https://eow.alc.co.jp/search?q=take+matters+into+one%27s+own+hands
  • http://d.hatena.ne.jp/A30/20160911/1473561461