Alun Cairns spoke at the last Welsh Questions in the House of Commons before the general election.
Plaid warned of a claw-back of powers.
Mr Cairns said the Great Repeal Bill would not see decisions taken away from the devolved bodies.
He reiterated that the UK government would temporarily hold on to powers for EU laws in areas like agriculture while discussions between the UK and devolved governments continue post-Brexit.
The proposal was set out by the UK government in its Great Repeal Bill, which proposes to transport EU laws to the UK statute book.
Opposition politicians from Labour, Plaid Cymru and the SNP raised concerns that devolution could be undermined by such a move.
The Shadow Welsh Secretary Christina Rees called for extra powers for the Joint Ministerial Council (JMC) to ensure that the Great Repeal Bill does not "in any way re-write or override devolution as set out in the recent Government of Wales Act".
The JMC is a group of senior ministers from the UK and devolved administrations.
The Plaid Cymru MP for Dwyfor Meirionnydd Liz Saville Roberts said that the UK government was planning to "claw-back devolution powers".
Mr Cairns said that the Great Repeal Bill proposals would not see any decisions currently taken by the Welsh Government "removed from them."
"We expect that repatriation of powers from the European Union will extend the powers of the WG significantly, but of course there is a process to work through in order to provide the stability and certainty that industry needs," said Mr Cairns.
The Great Repeal Bill has been criticised by First Minister Carwyn Jones and Plaid Cymru after ministers proposed a "holding pattern" for EU laws in areas like agriculture to go to the UK government temporarily first.
Devolved administrations will eventually see a "significant increase" in their decision-making power" after EU powers are repatriated to the UK, according to the secretary of state for Wales.