This is How Top Companies Successfully Scaled Agile and became successfull

Agile methodologies have been used successfully in many big companies, but it is often a challenge. There are many reasons: lack of project sponsorship, prolonged user validation, existing policies, legacy systems with no tests — and most importantly culture and inertia. Given all these obstacles how do you scale Agile processes in a big organization? Very carefully. If you’re interested in introducing Agile development practices into a large organization, you can try some of these techniques:

(i) Show don’t tell — Work on a project using Agile methods. Get it done on time and on budget using Agile methods.
(ii) Grow organically and incrementally — If you’re a manager it’s easy. Start with your team. Try to gain mindshare with your peer managers — for example, when collaborating on a project, suggest the use of Agile methods to coordinate deliverables and handoffs. If you’re a developer, try to convince your team members and manager to give it a try.
(iii) Utilize the organizational structure — Treat each team or department as a small Agile entity. If you can, establish well-defined interfaces.
(iv) Be flexible — Be willing to compromise and acknowledge other people’s concerns. Try to accommodate as much as possible even if it means you start with a hybrid Agile process. Changing people and their habits is hard. Changing the mindset of veteran people in big companies with established culture is extremely difficult.