The 31-year-old tested positive for Covid-19 on the eve of the Trent Bridge Test and was forced to watch the action from his hotel room.
Nevertheless, Williamson is back in the squad for the final Test at Headingley and has been cleared for action alongside Devon Conway and Michael Bracewell who also returned positive Covid-19 tests.
Speaking ahead of his return, the batsman said: "I watched a lot of it, I didn't have too much else to do.
"I don't shout at the TV, I watch and observe. It's always interesting seeing it from a different perspective, although it wasn't my preferable place to be. It was interesting to watch and connect from the other side a little bit.
"There was a lot of effort that went into the match and you do have to applaud the quality England have come in with. It was a Test where both teams put their front foot forward, played some shots.
"England are a strong side playing well so for us it's about improving as a side, the bigger picture. It's about focusing on our cricket and finding different areas of the game to target. The focus is on us and wanting to be better."
Williamson's return to the team allows the Kiwis to rebalance, with Henry Nicholls proving a vulnerable among specialist batters.
New Zealand could also shake-up the bowling attack, with Neil Wagner waiting for his first opportunity of the series.
His introduction could be at Tim Southee's expense following a disappointing performance in Nottingham.
Elsewhere, Ajaz Patel retains his spot in the 13-man squad.