Arizona Representative Gabrielle Giffords has formally resigned from the US Congress, receiving a standing ovation from her colleagues.

Ms Giffords, shot by a lone gunman during a constituency meeting in January 2011, announced on Sunday she was resigning to complete her recovery.

Before the ceremony, the House voted unanimously in favour of a final bill she introduced, on immigration.

In her resignation letter, Ms Giffords promised to return to public life.