The Indigenous affairs minister, Nigel Scullion, has announced that he will not recontest the next election, joining frontbenchers Michael Keenan and Kelly O’Dwyer in the list of high profile resignations from the Morrison government.

Scullion announced his decision on Australia Day, while the prime minister, Scott Morrison, was addressing the national citizenship ceremony in Canberra.

Scullion was elected senator for the Northern Territory in 2001 and was the leader of the National party in the Senate.

He has been a cabinet minister and the minister for Indigenous affairs since 2013, holding the position under the Abbott, Turnbull, and Morrison governments, and was minister for community services for the last year of the Howard government.

In a statement, Scullion thanked Morrison and the deputy prime minister, Nationals leader Michael McCormack, for asking him to stay on as Indigenous affairs minister until the election was called.

“It has been my privilege to have served as the minister for Indigenous affairs over the last five years,” he said. “I am grateful that Aboriginal and Torres Strait Islander people have welcomed me in every corner of this continent that I have visited, and worked with me in providing local and national solutions.”

The announcement comes one week after the shock resignation of senior Liberal frontbencher Kelly O’Dwyer, who said she was quitting politics for the “very personal reasons” of wanting to spend time with her two young children and to try for a third.

Her seat of Higgins in inner-city Melbourne covers an area that swung heavily to Labor in the November state election.

The human services minister, Michael Keenan, announced his resignation on Friday, saying he would not recontest his seat of Stirling in Western Australia, which he has held since 2004.

“I have always worked hard as a member of parliament and as a minister, but after doing this for 15 years, I cannot commit to another term,” he said in a statement on Friday.

“Over the Christmas break, it became very clear to me personally that times have changed and that this decision was the right one for my family and myself.”

Keenan said he has been “an absent father” and with a fourth child – a newborn – it was “unworkable” for his family.

“Whilst politics is a proud vocation, it is also difficult and exhausting business,” he said.

“The pressures on family life are formidable, as are the constant rigours of being an effective member of parliament, as well as a minister in the government.”

Keenan has previously held the justice and counter-terrorism portfolios.

He insisted he remained “resolutely optimistic” about the Coalition’s prospects at the election.

“We are sad to see him go, but entirely understand and respect the reasons for his decision,” finance minister Mathias Cormann said in a statement on Friday.

“Michael Keenan is a great mate, has made a wonderful contribution to public life both as a MP & a Minister, and most importantly is a terrific husband and father,” Defence Industry Minister Steven Ciobo said on Twitter.

– Australian Associated Press contributed to this story