He pointed to the troubles Mallard faced after wrongly accusing a parliamentary staffer of rape, and Mallard's attempts to drive out the protesters at Parliament with bad music on repeat in February.
"He took the Office of the Speaker only to have the worst approval rating of any politician in modern history. Now he's being rewarded for his bad behaviour."
Seymour said the timing of the announcement just before the 6pm news on a day in which there were other major stories at Parliament was "cynical".
"The Prime Minister and her colleagues should have shown leadership and integrity and not given in to Mallard's petty demands for an overseas posting.
"The only theory we can come up with is that Jacinda Ardern wanted to get rid of him and at least the Irish have a sense of humour."
The election of a new Speaker will also mean Question Time and the General Debate tomorrow are scrapped.
Earlier today, the National Party tried to get an additional Question Time and an additional debate scheduled for this week to replace it, but was unsuccessful.
That motion could have been big news for newly independent MP Gaurav Sharma who could be given time to speak in the House under privilege, allowing him to attack his former Labour colleagues without fear of defamation. Sharma was expelled from Labour's caucus this morning.
When Parliament meets tomorrow, the Government will put forward Deputy Speaker Adrian Rurawhe for the role of Speaker. Under Standing Orders, the rules that govern Parliament, the House will then adjourn for the day.
This would mean Question Time on Wednesday and General Debate will be cancelled. National is keen to ensure that does not happen, because it would mean the Prime Minister only being present for one session of Question Time this week - leaders typically skip Thursday sittings in favour of their deputies.
Cancelling General Debate would also be significant, given it is an opportunity for MPs to make more free-flowing speeches about any topics they choose.
Slots in general debate are allocated to political parties based on their representation in the House, but parties are allowed to give their slots away if they choose.
It is understood National had at least considered giving a slot to Sharma, a newly-independent MP. The party had previously given former Labour MP Louisa Wall one of its speaking slots on a debate on suicide after Labour denied Wall the opportunity to speak.
MPs speaking in the debating chamber are protected by parliamentary privilege. This means MPs can make defamatory statements without being held liable for what they say.
As Parliament finished Question Time on Tuesday, National's shadow leader of the house Chris Bishop sought leave "in light of other events … for the House to hold a General Debate after the dinner break" on Tuesday night, which would follow the format of the usual Wednesday debate.
There was objection to this motion, meaning it was not successful.
Bishop then sought leave for the House to hold a second Question Time on Thursday, again "in light of other events this week".
This Question Time would have replaced Wednesday's lost Question Time.
This was also voted down.
