He graduated from high school in June 2007 and returned to Golden Sunbeam as a teaching assistant where, in his spare time, he trained the pupils in basketball.

Under Ansah's mentoring, the Golden Sunbeam basketball team won several tournaments while playing international schools in Ghana.

When the West African Senior Secondary Certificate Examination (WASSCE) results became public, Ansah had 7 A's and a B in his business program.

Ansah applied to and was accepted at Brigham Young University with the help and support of Golden Sunbeam and the assistance of his friend, former ICT teacher and mentor Alma Ohene-Opare, who was at BYU at the time.

Alma Ohene-Opare and later Ken Frei played critical roles in helping Ansah adjust to his new surroundings and culture in a new country.

Unfamiliar with American football, Ansah had to be instructed in basic rules and techniques, even needing help getting on his pads for the first time.

[5] Midway through the 2010 season, Ansah made his first collegiate appearance in the Cougars' game versus Wyoming, where he recorded his first tackle.

[14] Coming out of college, Ansah was projected by analysts and scouts to be a first round draft selection and was a consensus top 10 pick.

[15] Although he was thought of as a raw talent who was a boom or bust prospect that lacked stamina, his large frame, size, quickness, athletic ability, consistency, and unparalleled length and foot speed made many feel he was too valuable to pass on.

[24] On September 22, 2013, Ansah earned his first career start after Jason Jones was placed on injured reserve for the remainder of the season with a knee injury.

He made a season-high seven combined tackles and sacked Robert Griffin III twice, one causing a fumble, in a 27–20 victory over the Washington Redskins.

In Week 12, he recorded two solo tackles and sacked Mike Glennon twice, as the Lions lost to the Tampa Bay Buccaneers 24–20.

[26] Ansah finished his rookie season with 32 combined tackles, 8 sacks, 2 forced fumbles, and a pass deflection in 14 games and 12 starts.

In the season opener against the New York Giants, he recorded an assisted tackle and was credited with half a sack on Eli Manning in a 35–14 victory.

On October 12, 2014, Ansah made five combined tackles and was credited with a season-high 2.5 sacks on Teddy Bridgewater, as the Detroit Lions defeated the Minnesota Vikings 17–3.

On January 4, 2015, Ansah started his first career playoff game and made two solo tackles and a sack on Tony Romo in a 24–20 loss to the Dallas Cowboys.

[26] Ansah started the Lions season opener against the San Diego Chargers and made two solo tackles and a sack on Philip Rivers in a 33–28 loss.

[26] On November 26, 2015, he racked up four combined tackles and was credited with a season-high 3 sacks on Mark Sanchez, as the Lions routed the Philadelphia Eagles 45–14.

[29] In the 2015 season, Ansah made 47 combined tackles, 14+1⁄2 sacks, 4 forced fumbles, and a pass deflection in 16 games and 16 starts.

During the wild card round against the Seattle Seahawks, Ansah made five combined tackles and sacked Russell Wilson twice, but the Lions lost 26–6.