When the Conservative Party finds itself in trouble, lawyer Arthur Hamilton is often the man tasked with the troubleshooting.

A soft-spoken figure in the courtroom, his quiet intensity hints at past achievements as a high-school athlete.

A former linebacker who was recruited to play for Greenville College in Illinois, Hamilton was hit from behind, which blew out his knee and left him unable to play competitive ball.

Instead, he returned to Canada, studied at the University of Toronto and became one of the top election law experts in the country, according to colleagues.

Now, the longtime Conservative Party lawyer has seen his name surface in connection with another scandal hitting the Conservative Party: on Monday, Senator Mike Duffy alleged that Hamilton is one of the people who helped negotiate payments to cover Duffy's expenses in the long-running Senate spending scandal. Duffy said Hamilton provided a cheque for $13,560 to cover his legal fees in the matter.

Hamilton's name has also come up over:

Accompanying witnesses in interviews with Elections Canada for the agency's investigation into misleading robocalls in Guelph, Ont., in the 2011 federal election.

A fierce defence of six Conservative MPs against a legal challenge that would have seen them removed from office over robocalls in their ridings. The federal court judge in the case said the respondent side of the case, led by Hamilton, engaged in "trench warfare" and made little effort to help Elections Canada investigate the allegations.

The married father of five-year-old twins still lives in his hometown in Toronto's east end. He has mainly kept a low profile, always declining interview requests, and politely refusing to go on television to summarize arguments made in high-profile but camera-free courtrooms.

Hamilton declined to comment on Duffy's allegations.

A spokesman for the Conservative Party suggested it's possible a cheque was cut to cover Duffy's legal expenses.

"At the time these legal expenses were incurred and paid, Mike Duffy was a member of the Conservative caucus. The Conservative Party sometimes assists members of caucus with legal expenses," Cory Hann said in an email to CBC News.

Long history with Conservative Party

Hamilton eschews coffee and alcohol, despite working punishing 16-hour days handling energy and resource regulation cases, as well as an increasing number of Conservative Party legal cases.

The Bay Street lawyer — Hamilton is a partner at Cassels Brock — has been involved with the Conservative Party from its inception, Conservative MP Erin O'Toole said in an interview with CBC News.

Hamilton helped with the legal work of merging the Canadian Alliance and the Progressive Conservatives, and represented the party against a legal challenge mounted by former PC cabinet minister Sinclair Stevens.

"I think Arthur's strong ability to litigate the case well, and the results were very positive, that I think led to him becoming very well-regarded in the party and with the leadership of the party," said O'Toole, a friend of Hamilton's since 2002.

Hamilton went on to represent the party as an intervener at the Gomery Commission in 2004 and 2005, and has been visible in smaller controversies prior to now, including being named in a lawsuit by former cabinet minister Helena Guergis (that suit was thrown out of court).

His zealous commitment to his client, however, has raised eyebrows.

While colleagues from the party and from his law firm agreed to interviews, it was tough to find a lawyer on the opposite side of the courtroom to speak on the record.

'Trench warfare'

Last winter, Hamilton led the response in the Federal Court for six Conservative MPs who saw their seats challenged. Ted Frankel, a partner at Cassels Brock, worked with Hamilton on the case.

"There aren’t many who do elections law in Canada. Arthur is one of the leaders in that field," said Frankel, who previously worked with Jack Siegel, a lawyer who has represented the Liberals on election law issues.

"Arthur is incredibly hard-working and he has an intensity that I think is pretty much unmatched by any other lawyer I’ve ever encountered."

That intensity led to some heated moments in the courtroom after Hamilton questioned the political leaning of a polling expert and accused the lawyer for the applicants of launching the case for political "payback."

Federal Court Judge Richard Mosley didn't overturn the election results, although he found that voter fraud occurred. But he did use the ruling to take to the Conservatives to task, represented by Hamilton.

"These proceedings have had partisan overtones from the outset. That was particularly evident in the submissions of the respondent MPs," Mosley wrote.

"In reviewing the procedural history and the evidence and considering the arguments advanced by the parties at the hearing, it has seemed to me that the applicants sought to achieve and hold the high ground of promoting the integrity of the electoral process while the respondent MPs engaged in trench warfare in an effort to prevent this case from coming to a hearing on the merits."

Frankel describes Hamilton as a social person and someone who's a "very, very strong proponent of the associates" (the more junior lawyers).

Identifies 'very strongly with the Conservative Party'

It may not surprise his detractors to hear that Hamilton is close to Jenni Byrne and Fred Delorey, respectively Prime Minister Stephen Harper's deputy chief of staff and the party's director of political operations. Both senior officials are known as staunch partisans.

Frankel says the zealous approach to defending his clients is one lawyers are taught to adopt on behalf of every client.

"But I think it comes even easier because he does identify very strongly with the Conservative Party and with the things that the prime minister wants to accomplish," Frankel said.

"He’s always working hard, whether it’s a big or a small file. He’s not one of those people who’s going to be caught napping on any sort of file. He’s always working every possible angle."

O'Toole and Frankel both praised Hamilton as principled and loyal.

Hamilton could have kept his athletic scholarship to Greenville, O'Toole said, even after his injury, but felt he would be taking a spot away at a small college that could have offered it to someone else.

"So he stepped away and returned to Canada. He's very much a person that will make decisions on principle and stand by them, which is what I like about him," O'Toole said.

As described by Frankel and O'Toole, Hamilton is a born advocate with a long memory. Those things fuel him more than anything else.

"Especially when people will be on one side or the other in a political argument or debate or in a courtroom, he has a long memory," O'Toole said.

"He doesn't take things personally, like a loss or anything like that, but I think he holds onto these things and probably finds motivation from them."