Ordained priest in May 1863 in Mechlin, Belgium, he left soon after to begin his missionary work in the area of Vancouver, British Columbia, Canada in November of that year.

In 1886, with two Jesuit priests, Pascal Tosi and Aloysius Robaut, and one layman, Frank Fuller, he sailed from Victoria with the intention of reaching the upper Yukon.

Father Tosi expressed concerns about this proposal, noting that Fuller had displayed signs of emotional instability.

He gave as his reasons for going ahead anyway as his wish to fulfill a promise made to the people of Nulato to return eight years earlier, and that there were stories that an Anglican priest, who was allegedly at St. Michael, Alaska, might arrive there and establish himself before Seghers.

As they continued down the river, Seghers came to realize that, as traveling conditions and the boat deteriorated, Fuller's mind did as well.

On 27 November, Seghers and Fuller, with two native guides they had acquired at Nuklukayet, decided to spend the night at the fish camp at what is today known as "Bishop's Rock".