Till is less formal than until and is used mainly in speech and informal writing. In academic writing and professional reports, until is much more frequent:
✗ Our government used the death penalty as a deterrent till 1989.
✓ Our government used the death penalty as a deterrent until 1989.
✗ He published a prose work and a few poems, but did not achieve success till he turned to play writing.
✓ He published a prose work and a few poems, but did not achieve success until he turned to play writing.
➡ until