The cross-code star was sent off with just 25 minutes on the clock during Saturday's match, after catching Lions wing Anthony Watson flush on the head with a shoulder charge.
All Blacks coach Steve Hansen confirmed Williams would plead guilty to a charge of unnecessary contact with the head when he faced a hearing at the New Zealand Rugby offices in Wellington on Sunday.
That hearing resulted in a four-week suspension being imposed on the centre, whose place in the All Blacks' squad for next weekend's decisive third Test has been taken by Malakai Fekitoa.