Yes he most likely did, but he denied it to save himself from Azkaban.
The Death Eaters that tortured the Longbottoms were Bellatrix, Rabastan and Rodolphus Lestrange, and Barty Crouch Jr. However, except for Bellatrix, most of them deny their involvement. It certainly seems, though, like the four Death Eaters were all caught in the act of torturing the Longbottoms, and were therefore unable to get themselves out of going to Azkaban.
‘You have been brought here before the Council of Magical Law,’ he said clearly, ‘so that we may pass judgement on you, for a crime so heinous –’
‘Father,’ said the boy with the straw-coloured hair. ‘Father … please …’ ‘– that we have rarely heard the like of it within this court,’ said Crouch, speaking more loudly, drowning out his son’s voice.
‘We have heard the evidence against you. The four of you stand accused of capturing an Auror – Frank Longbottom – and subjecting him to the Cruciatus Curse, believing him to have knowledge of the present whereabouts of your exiled master, He Who Must Not Be Named –’
‘Father, I didn’t!’ shrieked the boy in chains below. ‘I didn’t, I swear it, Father, don’t send me back to the Dementors –’
‘You are further accused,’ bellowed Mr Crouch, ‘of using the Cruciatus Curse on Frank Longbottom’s wife, when he would not give you information. You planned to restore He Who Must Not Be Named to power, and to resume the lives of violence you presumably led while he was strong. I now ask the jury –”
However, interestingly enough, both Dumbledore and Sirius Black say they personally don't know for sure.
“The Longbottoms were very popular,’ said Dumbledore. ‘The attacks on them came after Voldemort’s fall from power, just when everyone thought they were safe. Those attacks caused a wave of fury such as I have never known. The Ministry was under great pressure to catch those who had done it. Unfortunately, the Longbottoms’ evidence was – given their condition – none too reliable.’
‘Then Mr Crouch’s son might not have been involved?’ said Harry slowly.
Dumbledore shook his head. ‘As to that, I have no idea.”
Sirius isn't sure whether Crouch Jr. is guilty, but confirms that he was indeed found in the company of Death Eaters.
“Was his son a Death Eater?’ said Harry.
‘No idea,’ said Sirius, still stuffing down bread. ‘I was in Azkaban myself when he was brought in. This is mostly stuff I’ve found out since I got out. The boy was definitely caught in the company of people I’d bet my life were Death Eaters – but he might have been in the wrong place at the wrong time, just like the house-elf.”
Barty Crouch Jr. does confess himself to being a Death Eater, and plotting to restore the Dark Lord to power, when he's caught pretending to be Mad-Eye Moody. The Dark Lord hadn't been around for years to recruit new Death Eaters, and until that year the Death Eaters had been inactive. Barty Crouch Jr. refers to the Dark Lord as his master, and speaks of returning to his service, which proves that he would have have to been a Death Eater before the Dark Lord's fall.
“Then I had to be concealed. I had to be controlled. My father had to use a number of spells to subdue me. When I had recovered my strength, I thought only of finding my master … of returning to his service.”
Even more conclusively, the Dark Lord comes to find Barty Crouch Jr. and trusts him with an undercover mission, which he wouldn't have done if he wasn't actually a Death Eater.
“And then … and then …’ Crouch’s head rolled on his neck, and an insane grin spread across his face. ‘My master came for me. ‘He arrived at our house late one night, in the arms of his servant Wormtail. My master had found out that I was still alive.”
It's likely that Barty Crouch Jr. is at least somewhat overestimating how much the Dark Lord values him, but still, the Dark Lord does come and seek him out.
“She told him my father kept me imprisoned to prevent me seeking my master. And so my master knew that I was still his faithful servant – perhaps the most faithful of all. My master conceived a plan, based upon the information Bertha had given him. He needed me. He arrived at our house near midnight. My father answered the door.”
From this, we can see the Dark Lord trusted him enough to believe he could become Moody and help restore him to power. The Dark Lord does not trust easily, and wouldn't likely be willing to give such an important task to someone who hasn't proven his worth somehow.
“He asked me whether I was ready to risk everything for him. I was ready. It was my dream, my greatest ambition, to serve him, to prove myself to him. He told me he needed to place a faithful servant at Hogwarts.”
He also clearly craves the Dark Lord's approval.
“The Dark Lord and I,’ said Moody, and he looked completely insane now, towering over Harry, leering down at him, ‘have much in common. Both of us, for instance, had very disappointing fathers … very disappointing indeed. Both of us suffered the indignity, Harry, of being named after those fathers. And both of us had the pleasure … the very great pleasure … of killing our fathers, to ensure the continued rise of the Dark Order!”
He seeks more than just power or wealth, he wants the Dark Lord to honor and respect him.
“Turned it into a Portkey. My master’s plan worked. He is returned to power and I will be honoured by him beyond the dreams of wizards.”