The West Berkshire councillor went head-to-head with Labour's Tim Starkey after neither candidate won more than 50% of the vote in the first round of counting.
Mr Stansfeld, took a lead of 19,380 into the second round and ended 23,835 ahead of Mr Starkey - picking up 94,238 votes across the region's 16 districts.
The Tory had topped the polls in 13 districts in the first round, with Mr Starkey winning in Reading, Slough and Oxford.
Only 13.3% of eligible voters in the Thames Valley cast their ballots, with a turnout of 13.1% in Bracknell, 13.9% in Wokingham and 13.4% in Reading.
In Bracknell's first count, 3,939 out of 10,903 accepted votes put Mr Stansfeld as their first choice.
There were 342 spoiled ballots.
Mr Stansfeld will take up the £80,000-a-year role in May and his responsibilities will include setting the force's budget of around £400m and hiring and firing the chief constable.
The Thames Valley was one of more than 40 police force areas in England and Wales where commissioner elections have been taking place.
Independent candidate Geoff Howard finished third, with Lib Dem John Howson fourth, UKIP's Barry Cooper fifth and independent Patience Tayo Awe sixth.